refactor: Rewrite community feed as Feed class

[pselkirk]

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.39623% with 7 lines in your changes missing coverage. Please review.

Project coverage is 88.79%. Comparing base (c7f6bde) to head (85bd200). Report is 56 commits behind head on main.

Files with missing lines	Patch %	Lines
ietf/community/feeds.py	93.13%	7 Missing :warning:

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #7254    +/-   ##
========================================
  Coverage   88.78%   88.79%            
========================================
  Files         296      305     +9     
  Lines       41320    41543   +223     
========================================
+ Hits        36687    36889   +202     
- Misses       4633     4654    +21     

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