Tweak Chat Message CSS to center text

[ahuang11]

Before this PR, integer objects were not centered:

import panel as pn
pn.extension()

pn.Column(*[pn.chat.ChatMessage(i) for i in range(100)], height=500).show()

After:

Strings align properly with/without the change:

import panel as pn
pn.extension()

pn.Column(*[pn.chat.ChatMessage(f"{i}") for i in range(100)], height=500).show()

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5b5dda6) 84.66% compared to head (852cc2a) 84.67%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6135      +/-   ##
==========================================
+ Coverage   84.66%   84.67%   +0.01%     
==========================================
  Files         296      296              
  Lines       44160    44160              
==========================================
+ Hits        37388    37394       +6     
+ Misses       6772     6766       -6     

Flag	Coverage Δ
ui-tests	40.74% <ø> (+<0.01%)	⬆️
unitexamples-tests	72.58% <ø> (+<0.01%)	⬆️

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[philippjfr]

Makes total sense to me but can you confirm that this doesn't cause any issues with other content, markdown, images, etc.?

[ahuang11]

Since message class only gets added to Markdown, I think it doesn't cause issues: