@W-21952572: Add support for request level overrides

[stephendeoca]

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Description

Introduces request overrides that, when enabled, allow for config variables to be overriden

Motivation and Context

Additional granularity when configuring variables, allows for curated MCP experiences that go beyond the typical site / environment settings.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

How Has This Been Tested?

Unit tests and local valuation

Related Issues

Checklist

• I have updated the version in the package.json file by using npm run version. For example,
  use npm run version:patch for a patch version bump.
• I have made any necessary changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have documented any breaking changes in the PR description. For example, renaming a config
  environment variable or changing its default value.

Contributor Agreement

By submitting this pull request, I confirm that:

• I have read the CONTRIBUTING guidelines for this project and followed
  its Contribution Checklist.