feat: Allow agenda_note to be edited from the schedule editor

[jennifer-richards]

Fixes #3613 by providing an easy alternative to embedding extended descriptions in the session name.

Includes a migration to put old sessions marked as 'CANCELED' into the 'canceled' state. There are two sessions that appear to have been canceled that are not migrated automatically. These should be cleaned up manually.

>>> pp(list(Session.objects.with_current_status().exclude(current_status='canceled').filter(agenda_note__icontains='canceled').order_by('meeting__date').values_list('meeting__number', 'pk', 'agenda_note')))
[('75', 1179, 'Friday session Canceled'),
 ('75', 11179, 'Friday session Canceled'),
 ('79', 1722, 'Monday 1510-1610 CANCELED ONLY'),
 ('79', 11722, 'Monday 1510-1610 CANCELED ONLY')]

(The second and third entries are the ones indicated as being canceled.)

[codecov]

Codecov Report

Merging #5115 (90740b0) into main (bfe25fc) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #5115      +/-   ##
==========================================
+ Coverage   88.50%   88.51%   +0.01%     
==========================================
  Files         296      295       -1     
  Lines       40018    40015       -3     
==========================================
+ Hits        35416    35418       +2     
+ Misses       4602     4597       -5     

Impacted Files	Coverage Δ
ietf/meeting/forms.py	97.02% <ø> (ø)
ietf/meeting/views.py	90.70% <100.00%> (+<0.01%)	⬆️
ietf/secr/proceedings/proc_utils.py	86.33% <100.00%> (-0.09%)	⬇️
ietf/secr/sreq/forms.py	98.31% <100.00%> (+0.03%)	⬆️
ietf/secr/sreq/views.py	91.16% <100.00%> (-0.40%)	⬇️
ietf/nomcom/utils.py	91.54% <0.00%> (-0.49%)	⬇️
ietf/doc/views_search.py	89.02% <0.00%> (-0.42%)	⬇️
ietf/group/utils.py	94.17% <0.00%> (+0.44%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.