Update Sidebar navigation component

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### Description

<!-- Add a short description of your contribution. Consider adding
a checklist of variations, states, and breakpoints to the description so that reviewers can be sure to cross reference everything that has been completed. -->

Updating the `Sidebar` component to match the direction of the navigation changes from %"14.0" 

- Using the gray-900 color instead of having theme color influence the sidebar https://gitlab.com/gitlab-org/gitlab/-/issues/330467
- Using the name `Infrastructure` instead of `Kubernetes` in instances to reflect https://gitlab.com/gitlab-org/gitlab/-/issues/334011

### Figma file

<!-- Before pasting the link to your Figma file/frame, in the file sharing settings, make sure that “anyone with the link” can view. -->

[View working file in Figma →](https://www.figma.com/file/qEddyqCrI7kPSBjGmwkZzQ/branch/3wLvv6JyQvhy07Jxkvc630/Component-library?node-id=3050%3A0) `update-sidebar-component` branch

### Screenshots

Variants

| Before | After |
| ------ | ------ |
| ![image](/uploads/09701547d6b8b03ee1a32f4273042fd0/image.png) | ![image](/uploads/a0aed7fd48aa4851924daf691ad99c0b/image.png) |

Instances

| Before | After |
| ------ | ------ |
| ![image](/uploads/92de4216179a6d4983d028044a68bed7/image.png) | ![image](/uploads/8ea902918574292a8a156b2d984e558d/image.png) |

### Checklist

Make sure the following are completed before closing the issue:

1. [x] **Assignee**: Design in your working file. When applicable, follow our 
   [structure][structure], [building][building], and [annotation][annotation] guidelines. If you have any questions, reach out to a [FE/UX Foundations designer][foundations-team].
1. [x] **Assignee**: Update the link to the working file in the issue 
   description.
1. [x] **Assignee**: Ask a [FE/UX Foundations designer][foundations-team]
   to review your design (ensure they have edit permissions in Figma).
1. [x] **Reviewer**: Review and approve assignee’s design. Specific design 
   questions can be addressed with comments in Figma. Comment in this issue when the content is less specific to the design or requires greater visibility.
1. [x] **Reviewer**: Assign to a [Figma maintainer][figma-maintainer]
   for final review (make sure they have edit permissions in Figma).
1. [x] **Maintainer**: Review and approve assignee’s changes.
1. [x] **Maintainer**: Add the changes or additions to the target file. For 
   example, you’d copy a final chart design from the working file and paste into the related location in the Data Visualization file.
     1. [x] Ensure that all styles and components now belong to the target file.
     1. [x] For changes to the **Component Library** file, view the components in the Assets panel to ensure they align with our [asset library structure guidelines][structure].
1. [x] **Maintainer**: When applicable, [publish][publishing] any library 
   changes along with a clear commit message.
1. [x] **Assignee**: Move your working file to the shared Figma project:
     1. [ ] For Component Library changes, move your file to the [**Component archive**][component-archive] project.
     1. [ ] For all other changes, move your file to the [**Misc archive**][misc-archive] project.
     1. [ ] If you’re a community contributor, we ask that you [transfer ownership of your draft file](https://help.figma.com/hc/en-us/articles/360040530853) to the maintainer so they can move it to our archive, along with its version history and comments.
1. [-] **Assignee** (or Maintainer, for community contributions): If it’s a new
   pattern or a significant change, add an agenda item to the next UX weekly call to inform the team.
1. [-] **Assignee**: When applicable, [create an MR in this repository][new-gitlab-ui-mr] and apply the "component-guideline" template 
   to create or update the component’s documentation page. If you do not have capacity, [create an issue in this repository using the "Component documentation" issue template][pajamas-component-documentation-template]. Bring the issue to your team planning session for prioritization and scheduling. Mark the new issue as related to this one.
1. [x] **Assignee**: When applicable, [create an issue in GitLab UI using the "Component" issue template][gitlab-ui-component-template] to build or update the component code. Bring the issue to your team planning session for prioritization and scheduling. Mark the new issue as related to this one.
1. [x] **Assignee**: 🎉 Congrats, you made it! You can now close this issue.

[annotation]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/blob/main/doc/pajamas-ui-kit.md#adding-descriptions-notes-and-annotations
[building]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/blob/main/doc/pajamas-ui-kit.md#building-components
[foundations-team]: https://about.gitlab.com/company/team/?department=fe-ux-foundations-team
[figma-maintainer]: https://about.gitlab.com/handbook/engineering/projects/#design.gitlab.com
[publishing]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/blob/main/doc/pajamas-ui-kit.md#publishing-changes
[structure]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/blob/main/doc/pajamas-ui-kit.md#structure
[component-guideline-template]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/blob/main/.gitlab/merge_request_templates/component-guideline.md
[component-archive]: https://www.figma.com/files/project/5472112/Component-archive
[misc-archive]: https://www.figma.com/files/project/10620392/Misc-archive
[gitlab-ui-component-template]: https://gitlab.com/gitlab-org/gitlab-ui/-/issues/new?issuable_template=Component
[pajamas-component-documentation-template]: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/issues/new?issuable_template=Component%20documentation
[new-gitlab-ui-mr]: https://gitlab.com/gitlab-org/gitlab-ui/-/merge_requests/new

Story points: 2.0