fix: replace the phrase Teams Toolkit in the README with Microsoft 365 Agents Toolkit

[neil-yechenwei]

This PR is to replace the phrase Teams Toolkit in the README with Microsoft 365 Agents Toolkit for new UI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.93%. Comparing base (1654717) to head (9f9fc36).
⚠️ Report is 15 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev   #15640   +/-   ##
=======================================
  Coverage   92.93%   92.93%           
=======================================
  Files         623      623           
  Lines       38433    38433           
  Branches     7071     7126   +55     
=======================================
  Hits        35719    35719           
  Misses       1983     1983           
  Partials      731      731           

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