config: support HeadersList

[mattsains]

Fixes #6351

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.1%. Comparing base (130846a) to head (b2e073c).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #6657   +/-   ##
=====================================
  Coverage   73.0%   73.1%           
=====================================
  Files        189     189           
  Lines      15773   15807   +34     
=====================================
+ Hits       11525   11556   +31     
- Misses      3916    3918    +2     
- Partials     332     333    +1     

Files with missing lines	Coverage Δ
config/v0.3.0/config.go	89.6% <100.0%> (+1.1%)	⬆️
config/v0.3.0/log.go	95.5% <100.0%> (+0.2%)	⬆️
config/v0.3.0/metric.go	89.2% <100.0%> (+0.2%)	⬆️
config/v0.3.0/trace.go	97.4% <100.0%> (+0.1%)	⬆️

... and 2 files with indirect coverage changes

[pellared]

@codeboten, PTAL as a codeowner