Add rate limiting to the bastion feeder

[AlCutter]

This PR adds support for a configurable rate limiter to control incoming requests from the bastion.

For now, we'll just have a "global" rate limit per bastion, but if needed we can make this richer to support per log limits later.

Towards transparency-dev/armored-witness#253

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.

Project coverage is 33.69%. Comparing base (3c58af4) to head (fcb548b).
Report is 72 commits behind head on main.

Files	Patch %	Lines
internal/feeder/bastion/bastion_feeder.go	0.00%	5 Missing ⚠️
omniwitness/omniwitness.go	0.00%	3 Missing ⚠️
cmd/omniwitness/monolith.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #233       +/-   ##
===========================================
- Coverage   51.05%   33.69%   -17.36%     
===========================================
  Files          11       23       +12     
  Lines         903     1365      +462     
===========================================
- Hits          461      460        -1     
- Misses        374      810      +436     
- Partials       68       95       +27     

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