feat: show session purposes on the meeting request page

[rjsparks]

Fixes #4492

As the existing test for the view notes, the template output is almost impossible to test. It needs a refactor to allow it to be testable, but that effort is best applied when we move this out of /secr.

[codecov]

Codecov Report

Merging #5034 (33da77a) into main (570bd14) will increase coverage by 0.00%.
The diff coverage is 98.00%.

@@           Coverage Diff           @@
##             main    #5034   +/-   ##
=======================================
  Coverage   88.47%   88.48%           
=======================================
  Files         296      296           
  Lines       39818    39852   +34     
=======================================
+ Hits        35230    35263   +33     
- Misses       4588     4589    +1     

Impacted Files	Coverage Δ
ietf/meeting/views.py	90.69% <98.00%> (+0.12%)	⬆️
ietf/meeting/templatetags/proceedings_filters.py	88.23% <0.00%> (-5.89%)	⬇️
ietf/utils/pipe.py	82.60% <0.00%> (-4.35%)	⬇️
ietf/meeting/models.py	85.91% <0.00%> (-0.59%)	⬇️
ietf/group/models.py	92.30% <0.00%> (-0.37%)	⬇️
ietf/iesg/agenda.py	92.06% <0.00%> (+0.06%)	⬆️
ietf/utils/mail.py	79.85% <0.00%> (+0.23%)	⬆️
ietf/doc/views_search.py	89.64% <0.00%> (+0.41%)	⬆️
ietf/group/utils.py	94.17% <0.00%> (+0.44%)	⬆️
ietf/nomcom/utils.py	91.78% <0.00%> (+0.48%)	⬆️
... and 1 more

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