feat: Add serializer for comments in feed

[gzurowski]

Add an initial implementation of a serializer for comments:

Example:

 {
      "id": 363,
      "content_type": "RHCOMMENTMODEL",
      "content_object": {
        "comment_content_json": {
          "ops": [
            {
              "insert": "Letsfdohsdgfshousfdg oh;\n"
            }
          ]
        },
        "comment_content_type": "QUILL_EDITOR",
        "comment_type": "GENERIC_COMMENT",
        "document_type": "PAPER",
        "hub": {
          "name": "Neuroscience",
          "slug": "neuroscience"
        },
        "id": 80,
        "parent_id": null,
        "thread_id": 80
      }

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 6 lines in your changes missing coverage. Please review.

Project coverage is 68.55%. Comparing base (538c7eb) to head (3861704).
Report is 43 commits behind head on master.

Files with missing lines	Patch %	Lines
src/feed/serializers.py	84.00%	4 Missing ⚠️
src/feed/signals/comment_signals.py	96.00%	1 Missing ⚠️
src/feed/tasks.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2138      +/-   ##
==========================================
+ Coverage   67.77%   68.55%   +0.78%     
==========================================
  Files         427      428       +1     
  Lines       23586    23013     -573     
==========================================
- Hits        15985    15777     -208     
+ Misses       7601     7236     -365     

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud