Issue:
refactor: use lowercase names for run environment and config files

## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [x] Refactoring
- [ ] Dependency updates

## Description
<!-- Describe your changes in detail -->
This PR updates the `RUN_ENV` environment variable and config files to use `lowercase` names instead of `PascalCase` names. In addition, this fixes the values of `SCHEDULER_FLOW` environment variable in the `Dockerfile` and release workflows to use `snake_case` names instead of `PascalCase` names, since the code expected the names to be `snake_case` already.

### Additional Changes

- [ ] This PR modifies the database schema
- [x] This PR modifies application configuration/environment variables

<!-- 
Provide links to the files with corresponding changes.

Following are the paths where you can find config files:
1. `config`
2. `crates/router/src/configs`
3. `loadtest/config`
-->
This updates the file names for config files to use their lowercase names instead. This could break our sandbox environment for this reason.

## Motivation and Context
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Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.

If you don't have an issue, we'd recommend starting with one first so the PR
can focus on the implementation (unless its an obvious bug or documentation fix
that will have little conversation).
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This decision originated from the discussion at https://github.com/juspay/hyperswitch/pull/794#discussion_r1144947357 when I was working on the PR.

## How did you test it?
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Did you write an integration/unit/API test to verify the code changes?
Or did you test this change manually (provide relevant screenshots)?
-->
Built Docker images, verified things work as expected.

## Checklist
<!-- Put an `x` in the boxes that apply -->

- [x] I formatted the code `cargo +nightly fmt --all`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed submitted code
- [ ] I added unit tests for my changes where possible
- [ ] I added a [CHANGELOG](/CHANGELOG.md) entry if applicable


Resolution:
<think>
PR Context:
- Title: doc:Changelog for release v0.5.7
- Merged: 2023-04-19T08:01:28Z
- Files changed: 1 files
- Commits: 4 commits

Implementation approach:
# 0.5.7 (2023-04-18)

## New Features

* **connector:**
  *  [Shift4] add support for card 3DS payment (#828) (29999fe5)
  *  [Nuvei] add support for card mandates (#818) (298a0a49)
* **bank_redirects:**  modify api contract for sofort (#880) (fc2e4514)
  *  add template code for connector forte (#854) 
## Bug Fixes

* **connector:**  [coinbase] make metadata as option parameter (#887) (f5728955)
*  Update events table after notifying merchant (#871) (ba013026)
* **stripe:**  remove
</think>

To implement this, you'll need to modify:


(No detailed commit information available)