Fix bug with case sensitivity tied to github handles

[amrit110]

This pull request standardizes the handling of GitHub handles throughout the codebase by normalizing them to lowercase. This ensures case-insensitive matching for all Firestore lookups and API payloads, reducing potential issues caused by case differences in GitHub usernames. The changes affect both the backend service and utility functions.

GitHub handle normalization:

• Added a new utility function normalize_github_handle in src/aieng_platform_onboard/utils.py to convert GitHub handles to lowercase for consistent lookups.
• Updated Firestore queries in get_participant_data, check_onboarded_status, and update_onboarded_status to use normalized GitHub handles, ensuring case-insensitive document retrieval and updates. [1] [2] [3]
• Modified the payload in fetch_token_from_service to send the normalized GitHub handle to the backend API.

Backend service update:

• Updated get_github_handle_from_workspace_sa in services/token-service/main.py to normalize GitHub handles before Firestore lookups and in return values, ensuring consistent participant identification. [1] [2]

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.09%. Comparing base (5939481) to head (b769ed9).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #33      +/-   ##
==========================================
+ Coverage   87.96%   88.09%   +0.13%     
==========================================
  Files           3        3              
  Lines         457      462       +5     
==========================================
+ Hits          402      407       +5     
  Misses         55       55              

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