SetupDataPkg/ConfigKnobShimPeiLib: Revert ConfigKnobShimPeiLib change and fix unit test.

[apop5]

Description

Commit #369 erroneously removed the implementation for GetConfigKnobOverride from ConfigKnobShimPeiLib. Adding back the implementation to PEI and fixing the unit test to correctly work, in the same fashion as Dxe/MM versions.

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, ...
• [ ] 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

Mu Oem sample was failing with an unresolved external GetConfigKnobOverride for X64 PEI. After making this change, the unresolved external was resolved.

Integration Instructions

N/A

[apop5]

@os-d

Can you double check if this is acceptable?

[codecov-commenter]

Codecov Report

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

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:exclamation: Current head fcfef99 differs from pull request most recent head 23e1224

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #371 +/- ## ======================================= Coverage ? 36.22% ======================================= Files ? 31 Lines ? 6258 Branches ? 449 ======================================= Hits ? 2267 Misses ? 3989 Partials ? 2 ``` | [Flag](https://app.codecov.io/gh/microsoft/mu_feature_config/pull/371/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/371/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=microsoft) | `27.56% <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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