[chore] add internal/common to CODEOWNERS and part of selection

[atoulme]

Add a metadata.yaml file to internal/common to set it as part of CODEOWNERS. This will allow us to remove it from the .github/ALLOWLIST file.

[atoulme]

"internal/common" has an entry in CODEOWNERS file
There are 1 component(s) that have owners but are present in ALLOWLIST file

Looks like we'll need to update the template used by githubgen first before this goes in.

[atoulme]

This can be fixed with open-telemetry/opentelemetry-go-build-tools#669