Exclude test data from functions endpoint response

[kshyju]

This PR modifies both read and write operations related to test data for functions.

1. When the /admin/functions/{name} PUT operation is called, the "TestData" property will no longer be saved. The response object for this call will not include "TestData" property populated.
2. When the admin/functions/{name} GET operation is called, the "TestData" property will no longer be included in the API response.

These changes are gated behind a feature flag, which is disabled (set to false) by default. We will begin by enabling this feature on a few stamps and, upon confirming its effectiveness, will roll it out more broadly. In a future release, we plan to remove the feature flag and enable this change by default.

Pull request checklist

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Otherwise: Link to backporting PR - [in-proc] Exclude test data from functions endpoint response (#10943) #10981
• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• I have added all required tests (Unit tests, E2E tests)

[fabiocav]

@microsoft-github-policy-service rerun

[mathewc]

Looks good - thanks Shyju!