feat: re-consolidate html sanitizing

[noralmaani]

Uses nh3 for html sanitization. This uses two linkers: a markdown extension and Django's urlize filter for templates, dropping the linkify filter that used bleach's linker for both contexts.

Introduces a nooperner noferrer rel attribute to links as the default nh3 param.

Fixes #10138. This also renders mailman URLs and fixes #10120.

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.71%. Comparing base (e756948) to head (c8d1fd2).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
ietf/utils/markdown.py	89.36%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #11641   +/-   ##
=======================================
  Coverage   88.71%   88.71%           
=======================================
  Files         335      335           
  Lines       45256    45257    +1     
=======================================
+ Hits        40151    40152    +1     
  Misses       5105     5105           

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