otelgin: Refactor option type

[pellared]

Why

Per #851

What

Adhere to https://github.com/open-telemetry/opentelemetry-go/blob/main/CONTRIBUTING.md#configuration

[codecov]

Codecov Report

Merging #857 (6a28822) into main (718a4aa) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main    #857   +/-   ##
=====================================
  Coverage   79.1%   79.1%           
=====================================
  Files         62      62           
  Lines       2744    2747    +3     
=====================================
+ Hits        2172    2175    +3     
  Misses       440     440           
  Partials     132     132           

Impacted Files	Coverage Δ
...ation/github.com/gin-gonic/gin/otelgin/gintrace.go	78.6% <100.0%> (ø)
...ntation/github.com/gin-gonic/gin/otelgin/option.go	100.0% <100.0%> (ø)