feat: task + API for rfc-index creation

[jennifer-richards]

Adds a task and an API to trigger creation of a fresh rfc-index

[codecov]

Codecov Report

❌ Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.37%. Comparing base (1799245) to head (482b692).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
ietf/sync/tasks.py	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10537      +/-   ##
==========================================
- Coverage   88.39%   88.37%   -0.03%     
==========================================
  Files         326      327       +1     
  Lines       43813    44089     +276     
==========================================
+ Hits        38730    38965     +235     
- Misses       5083     5124      +41     

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