Allow overriding area repr map section HTML

[djhoese]

These changes help control how AreaDefinitions and others are represented when plotted for sphinx documentation (specifically Satpy). See pytroll/satpy#2864 for more information. No TDD on this one.

CC @BENR0

• Closes #xxxx
• Tests added
• Tests passed
• Fully documented

[codecov]

Codecov Report

Attention: Patch coverage is 96.77419% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.97%. Comparing base (0a47fd3) to head (8002a7a).
Report is 62 commits behind head on main.

Files with missing lines	Patch %	Lines
pyresample/_formatting_html.py	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #615      +/-   ##
==========================================
- Coverage   93.97%   93.97%   -0.01%     
==========================================
  Files          86       86              
  Lines       13819    13825       +6     
==========================================
+ Hits        12987    12992       +5     
- Misses        832      833       +1     

Flag	Coverage Δ
unittests	93.97% <96.77%> (-0.01%)	⬇️

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[coveralls]

coverage: 93.676% (-0.004%) from 93.68%
when pulling 8002a7a on djhoese:feat-html-bokeh
into af0d4cc on pytroll:main.

[mraspaud]

LGTM