feat: move IETF Activity reports from external text based to HTML pages

[rpcross]

No description provided.

[jennifer-richards]

Comments are inline. I think there's a mustfix fencepost error on the end date handling plus some smaller stuff.

[codecov]

Codecov Report

Merging #5180 (9d76281) into main (ce374ac) will increase coverage by 0.02%.
The diff coverage is 85.29%.

@@            Coverage Diff             @@
##             main    #5180      +/-   ##
==========================================
+ Coverage   88.54%   88.56%   +0.02%     
==========================================
  Files         295      294       -1     
  Lines       40110    40087      -23     
==========================================
- Hits        35516    35505      -11     
+ Misses       4594     4582      -12     

Impacted Files	Coverage Δ
ietf/iesg/urls.py	100.00% <ø> (ø)
ietf/meeting/urls.py	81.25% <ø> (ø)
ietf/meeting/views.py	91.13% <80.00%> (+0.27%)	⬆️
ietf/iesg/views.py	92.53% <85.18%> (-0.71%)	⬇️
ietf/secr/proceedings/proc_utils.py	86.33% <100.00%> (ø)
ietf/utils/fields.py	91.75% <100.00%> (ø)
ietf/nomcom/utils.py	91.30% <0.00%> (-0.25%)	⬇️
ietf/meeting/helpers.py	89.84% <0.00%> (-0.07%)	⬇️
ietf/person/models.py	91.91% <0.00%> (ø)
ietf/doc/views_search.py	89.25% <0.00%> (ø)
... and 3 more

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