feat: render charters on about page using markdown

[rjsparks]

Remember the /group/<acronym>/about/rendertest view for a before/after comparison. (This PR fixes a js issue in that view).

The last time we pressed people to look at rendertest, I don't think we were using nl2br, so some of the really old charters with strange linebreaks in their text files will still just look strange, but overall, using it will likely produce the least surprise.

cc: @larseggert

[codecov]

Codecov Report

Merging #5795 (c3da308) into main (6737095) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #5795      +/-   ##
==========================================
- Coverage   88.67%   88.67%   -0.01%     
==========================================
  Files         288      288              
  Lines       39936    39937       +1     
==========================================
  Hits        35413    35413              
- Misses       4523     4524       +1     

Impacted Files	Coverage Δ
ietf/group/views.py	90.96% <100.00%> (+<0.01%)	⬆️

... and 3 files with indirect coverage changes

[rjsparks]

@larseggert wants to see if he can tweak this for minor improvements before it is merged.

[larseggert]

I don't think there is anything more I can easily do. Fixing the oddities would entail switching libs and/or writing custom plugins.

[rjsparks]

Mutter: foot-gunned by the GH stateful type-of-merge button once again...