Add TextMapPropagator function to autoprop

[MrAlias]

Resolve #2590

The collector plans to add configuration that will use a propagator describe in a text configuration file. That text needs to be converted into a propagator. This adds the GetTextMapPropagator function to do that conversion.

[codecov]

Codecov Report

Merging #2593 (6387ee4) into main (0be7156) will not change coverage.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main   #2593   +/-   ##
=====================================
  Coverage   74.3%   74.3%           
=====================================
  Files        144     144           
  Lines       6569    6569           
=====================================
  Hits        4883    4883           
  Misses      1543    1543           
  Partials     143     143           

Impacted Files	Coverage Δ
propagators/autoprop/propagator.go	100.0% <100.0%> (ø)
propagators/autoprop/registry.go	100.0% <100.0%> (ø)