[Feature Flag] Enable `new_ci_provisioning` flag

<!-- Title suggestion: [Feature flag] Enable description of feature -->

# Summary

<!-- Short description of what the feature is about and link to relevant other issues. -->

This issue is to rollout the new [CI minutes provisioning](https://gitlab.com/groups/gitlab-org/-/epics/5715) on CustomersDot production,
that is currently behind the [`new_ci_provisioning`](https://gitlab.com/gitlab-org/customers-gitlab-com/-/feature_flags/102/edit) feature flag.

## Owners

- Team: ~"group::utilization" 
- Most appropriate Slack channel to reach out to: `#g_utilization`
- Best individual to reach out to: `@vij`
- PM: `@amandarueda` 

## The Rollout Plan

- Rollout Feature for everyone as soon as it's ready

This feature is running in parallel with existing provisioning and as such is as yet unused on GitLab.com so it can roll out to everyone whilst we monitor and validate the data being created.

## Expectations

### What are we expecting to happen?

We will expect to start seeing API requests in the Kibana logs, between CustomersDot and GitLab.

This will result in the creation of `Ci::Minutes::AdditionalPack` records on GitLab when minutes are purchased, and updates to those packs when linked namespaces are changed.

### What might happen if this goes wrong?

We may see an increase in errors if an unforeseen scenario occurs.

The result of this would be incorrect data being applied in GitLab.com, the severity of which is low because the data is as yet unused and we have a separate rake task for re-syncing the same data which can always run if/when the problem is resolved.

We can disable the feature flag safely if this occurs, which will prevent further data creation.

### What can we monitor to detect problems with this?

We can/should monitor the following after enabling:

**Staging:**

- [#s_fulfillment_status](https://gitlab.slack.com/archives/CL7SX4N86)
- [Kibana logs for API endpoints](https://nonprod-log.gitlab.net/goto/2b4f611b3e6c912061b19e1502722cf5)
- [Create packs Sentry](https://sentry.gitlab.net/gitlab/customersgitlabcom/?query=is%3Aunresolved+syncminutesjob)
- [Transfer packs Sentry](https://sentry.gitlab.net/gitlab/customersgitlabcom/?query=is%3Aunresolved+transfer)


**Production:**

- [#s_fulfillment_status](https://gitlab.slack.com/archives/CL7SX4N86)
- [Kibana logs for API endpoints](https://log.gprd.gitlab.net/goto/dad196f12169b034bd809671da17fb2b)
- [Create packs Sentry](https://sentry.gitlab.net/gitlab/customersgitlabcom/?query=is%3Aunresolved+syncminutesjob)
- [Transfer packs Sentry](https://sentry.gitlab.net/gitlab/customersgitlabcom/?query=is%3Aunresolved+transfer)

## Rollout Steps

### Rollout on non-production environments

- [x] Ensure that the feature MRs have been deployed to non-production environments, i.e. `customers-staging`.
- [x] Enable the feature globally on non-production environments by applying the appropriate environment, e.g. `customers-staging` and `customers-development`.
- [x] Verify that the feature works as expected. Posting the QA result in this issue is preferable.

### Preparation before production rollout

- [x] Ensure that the feature MRs have been deployed to production
- [x] Check if the feature flag change needs to be accompanied with a
  [change management issue](https://about.gitlab.com/handbook/engineering/infrastructure/change-management/#feature-flags-and-the-change-management-process).
  Cross link the issue here if it does.
- [x] Ensure that you or a representative in Fulfillment can be available for at least 2 hours after feature flag updates in production.
  If a different developer will be covering, or an exception is needed, please inform the Fulfillment team in #s_fulfillment_engineering
- [x] Ensure any documentation has been updated
- [x] If the feature might impact the user experience, notify `#s_fulfillment` and potentially `#support_gitlab-com`, as well as your team channel ([more guidance when this is necessary in the dev docs](https://docs.gitlab.com/ee/development/feature_flags/controls.html#communicate-the-change)).

### Global rollout on CustomersDot production

- [x] Confirm the feature flag is enabled on `staging` without incident
- [ ] Roll out the feature to targeted testing users first (if applicable)
- [ ] If applicable, [incrementally roll out](https://docs.gitlab.com/ee/operations/feature_flags.html#percent-rollout) the feature.
- [ ] Verify the change has the desired outcome with the limited rollout before enabling the feature globally on production.
- [x] Enable the feature globally on production environment 
- [x] Wait for [at least one day for the verification term](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#including-a-feature-behind-feature-flag-in-the-final-release).

### Release the feature

After the feature has been [deemed stable](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#including-a-feature-behind-feature-flag-in-the-final-release),
the clean up should be done as soon as possible to permanently enable the feature and reduce complexity in the codebase.

<!-- The checklist here is to help stakeholders keep track of the feature flag status -->
- [x] Create a merge request to remove `new_ci_provisioning` feature flag
  - [x] Remove all references to the feature flag from the codebase
- [x] Ensure that the cleanup MR has been deployed to both staging and production
- [x] Disable the feature flag via the [CustomersDot dashboard](https://gitlab.com/gitlab-org/customers-gitlab-com/-/feature_flags)
- [x] Ensure production environment is still working as expected
- [x] Remove the [Unleash feature flag](https://gitlab.com/gitlab-org/customers-gitlab-com/-/feature_flags/102/edit)
- [x] Close this rollout issue.

## Rollback Steps

- [ ] This feature can be disabled by performing the following actions:
  - [ ] Disable the Unleash flag on the [feature flag page](https://gitlab.com/gitlab-org/customers-gitlab-com/-/feature_flags/102/edit)

Story points: 1.0