config: add support for Insecure

[mattsains]

fixes #6351

Based on spec here: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/exporter.md#configuration-options (search "Insecure")

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.9%. Comparing base (8129e89) to head (3210496).
Report is 2 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #6658   +/-   ##
=====================================
  Coverage   73.9%   73.9%           
=====================================
  Files        195     195           
  Lines      16671   16671           
=====================================
  Hits       12332   12332           
  Misses      3980    3980           
  Partials     359     359           

Files with missing lines	Coverage Δ
config/v0.3.0/log.go	95.3% <100.0%> (ø)
config/v0.3.0/metric.go	89.0% <100.0%> (ø)
config/v0.3.0/trace.go	97.3% <100.0%> (ø)

... and 1 file with indirect coverage changes

[pellared]

@codeboten, PTAL as a codeowner

[mattsains]

@codeboten I think I need your approval to get this PR to merged