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 55.90909% with 97 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.79%. Comparing base (6ffd50b) to head (d431395).

Files with missing lines	Patch %	Lines
gcc/delay_rate_controller.go	40.00%	51 Missing ⚠️
gcc/send_side_bwe.go	0.00%	42 Missing ⚠️
gcc/overuse_detector.go	92.15%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##              main      #34       +/-   ##
============================================
- Coverage   100.00%   76.79%   -23.21%     
============================================
  Files            6       10        +4     
  Lines          198      418      +220     
============================================
+ Hits           198      321      +123     
- Misses           0       97       +97     

Flag	Coverage Δ
go	76.79% <55.90%> (-23.21%)	⬇️

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