Move Go website_docs into opentelemetry.io repo

[chalin]

• Closes Move Go and Ruby docs into this repo #1935
• Contributes to Move website_docs to OTel website repo opentelemetry-go#4214
• Steps:
  • Refreshed git rm content-modules/opentelemetry-go
  • Copied pages: cp -R content-modules/opentelemetry-go/website_docs content/en/docs/instrumentation/go
  • Updated _index.md:
    • Removed github_repo and other cascaded page-meta front-matter fields
    • Replaced use of lang_instrumentation_index_head by new shortcode
  • git rm content-modules/opentelemetry-go
• Drops hugo.yaml mount point of Go submodule
• Cleans up Prettier ignore file to eliminate special Go submodule rules
• Adds appropriate entry for @open-telemetry/go-instrumentation-approvers to CODEOWNERS
• Deleted now obsolete lang_instrumentation_index_head shortcode.

---

Preview: https://deploy-preview-2872--opentelemetry.netlify.app/docs/instrumentation/go/

No changes to the generated site files (aside from redirect-rule reordering) after the files got moved:

$ (cd public && git diff -- . ':(exclude)*.xml') | grep ^diff  
diff --git a/_redirects b/_redirects

/cc @MrAlias

[cartermp]

🎉