config: add support for extra TLS configuration

[mattsains]

Added support for configuring:

• ClientCertificate
• ClientKey

Based on #6376
Partially addresses #6351

[codecov]

Codecov Report

Attention: Patch coverage is 91.30435% with 4 lines in your changes missing coverage. Please review.

Project coverage is 68.5%. Comparing base (958c959) to head (58ab334).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
config/v0.3.0/config.go	81.8%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6378     +/-   ##
=======================================
- Coverage   68.5%   68.5%   -0.1%     
=======================================
  Files        200     200             
  Lines      16781   16791     +10     
=======================================
+ Hits       11503   11509      +6     
- Misses      4933    4936      +3     
- Partials     345     346      +1     

Files with missing lines	Coverage Δ
config/v0.3.0/log.go	95.3% <100.0%> (ø)
config/v0.3.0/metric.go	85.8% <100.0%> (ø)
config/v0.3.0/trace.go	97.3% <100.0%> (ø)
config/v0.3.0/config.go	85.0% <81.8%> (+0.6%)	⬆️

... and 1 file with indirect coverage changes

[mattsains]

@dmathieu would you be able to re-approve this? I updated it against main

[mattsains]

@dmathieu would appreciate another approval - I think last time you might have forgotten to hit the button, because I didn't see a new approval after you thumbsup'd my comment

[dmathieu]

I'm approving the CI. But you don't need another PR approval from me. We do need an approval from another approver though.