feat: create docevents for adding/removing obs/updates

[rudimatz]

add log entries like this for obs and updates relations

[rudimatz]

relates to #10851, which contains the main logic... this only adds DocEvents for the history tab in DT

[rudimatz]

possibly OBE, will turn into draft

[rudimatz]

see also #10851 (review) for post-MVP fix

[codecov]

Codecov Report

❌ Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.49%. Comparing base (e37a2c9) to head (dab2714).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
ietf/api/serializers_rpc.py	0.00%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10898      +/-   ##
==========================================
- Coverage   88.51%   88.49%   -0.02%     
==========================================
  Files         332      332              
  Lines       44970    44980      +10     
==========================================
  Hits        39807    39807              
- Misses       5163     5173      +10     

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