feat: add FEATURE_ENABLE_CHAT_V2_ENDPOINT to environment files and update library version

[mraman-2U]

This pull request introduces a new feature flag for enabling a chat V2 endpoint across multiple environments and updates a dependency version in package.json. Below is a summary of the key changes:

Feature Flag Addition:

• Added FEATURE_ENABLE_CHAT_V2_ENDPOINT to the .env file with an empty value for production configuration.
• Added FEATURE_ENABLE_CHAT_V2_ENDPOINT='false' to the .env.development file for local development.
• Added FEATURE_ENABLE_CHAT_V2_ENDPOINT='false' to the .env.test file for testing environments.

Dependency Update:

• Updated the version of @edx/frontend-lib-learning-assistant from ^2.20.0 to ^2.22.0 in package.json.…pdate frontend-lib-learning-assistant version

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.33%. Comparing base (06902d8) to head (bf57318).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1768   +/-   ##
=======================================
  Coverage   90.33%   90.33%           
=======================================
  Files         344      344           
  Lines        5793     5793           
  Branches     1394     1391    -3     
=======================================
  Hits         5233     5233           
  Misses        541      541           
  Partials       19       19           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[ilee2u]

Just a quick note, GitHub actions require a blank line at the end of all files to run properly.

[mraman-2U]

Update the env files with a blank line at the end.