Add ChatInterface button tooltips

[ahuang11]

Mainly useful if show_button_name is disabled.

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.79%. Comparing base (1f821d6) to head (0643332).
Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
panel/tests/ui/chat/test_chat_interface_ui.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7552      +/-   ##
==========================================
- Coverage   82.38%   81.79%   -0.59%     
==========================================
  Files         339      339              
  Lines       50995    51329     +334     
==========================================
- Hits        42010    41985      -25     
- Misses       8985     9344     +359     

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