Add delay rate controller

[mengelbart]

The delay rate controller updates the rate as described here: https://datatracker.ietf.org/doc/html/draft-ietf-rmcat-gcc-02#section-5.5

[codecov]

Codecov Report

❌ Patch coverage is 73.12500% with 43 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.91%. Comparing base (a9f4688) to head (aedae8e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
gcc/delay_rate_controller.go	57.00%	42 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #34      +/-   ##
==========================================
- Coverage   98.48%   88.91%   -9.57%     
==========================================
  Files           7        9       +2     
  Lines         264      424     +160     
==========================================
+ Hits          260      377     +117     
- Misses          2       44      +42     
- Partials        2        3       +1     

Flag	Coverage Δ
go	88.91% <73.12%> (-9.57%)	⬇️

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