config: support HeadersList

[mattsains]

Fixes #6351

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.6%. Comparing base (764a633) to head (c5dafcb).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #6657   +/-   ##
=====================================
  Coverage   75.5%   75.6%           
=====================================
  Files        207     207           
  Lines      19152   19186   +34     
=====================================
+ Hits       14475   14506   +31     
- Misses      4241    4243    +2     
- Partials     436     437    +1     

Files with missing lines	Coverage Δ
config/v0.3.0/config.go	89.7% <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 1 file with indirect coverage changes

[pellared]

@codeboten, PTAL as a codeowner

[pellared]

How about updating these two files:

• config/testdata/v0.3.yaml
• config/testdata/v0.3.json

so that they include the new supported fields?

[mattsains]

How about updating these two files:

• config/testdata/v0.3.yaml
• config/testdata/v0.3.json

so that they include the new supported fields?

They already are in the config files but so far have been unsupported by the code. That’s what inspired me to create this PR in the first place

[pellared]

Looks goods 👍 Please resolve the conflicts.

[codeboten]

Thanks @mattsains!