Add Multiple Config Environment Build Support

[os-d]

Description

This updates the UpdateConfigHdr.py plugin to be able to generate multiple config headers from multiple XML files to support the use case where one PlatformBuild.py file is producing multiple config environments, such as non-secure world and StMM. This is backwards compatible with platforms that only build a single config environment.

For each item, place an "x" in between [ and ] if true. Example: [x]. (you can also check items in the GitHub UI)

• [ ] Impacts functionality?
  • Functionality - Does the change ultimately impact how firmware functions?
  • Examples: Add a new library, publish a new PPI, update an algorithm, ...
• [ ] Impacts security?
  • Security - Does the change have a direct security impact on an application, flow, or firmware?
  • Examples: Crypto algorithm change, buffer overflow fix, parameter validation improvement, ...
• [ ] Breaking change?
  • Breaking change - Will anyone consuming this change experience a break in build or boot behavior?
  • Examples: Add a new library class, move a module to a different repo, call a function in a new library class in a pre-existing module, ...
• [ ] Includes tests?
  • Tests - Does the change include any explicit test code?
  • Examples: Unit tests, integration tests, robot tests, ...
• [x] Includes documentation?
  • Documentation - Does the change contain explicit documentation additions outside direct code modifications (and comments)?
  • Examples: Update readme file, add feature readme file, link to documentation on an a separate Web page, ...

How This Was Tested

Tested on a platform with multiple config environments and with a single.

Integration Instructions

See docs in this PR.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 35.92%. Comparing base (11f63c3) to head (9d36c4a).

:exclamation: Current head 9d36c4a differs from pull request most recent head 6017244

Please upload reports for the commit 6017244 to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #374 +/- ## ======================================= Coverage 35.92% 35.92% ======================================= Files 31 31 Lines 6319 6319 Branches 669 669 ======================================= Hits 2270 2270 Misses 4043 4043 Partials 6 6 ``` | [Flag](https://app.codecov.io/gh/microsoft/mu_feature_config/pull/374/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=microsoft) | Coverage Δ | | |---|---|---| | [Linux](https://app.codecov.io/gh/microsoft/mu_feature_config/pull/374/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=microsoft) | `27.24% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=microsoft#carryforward-flags-in-the-pull-request-comment) to find out more.

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