Move github detector to use semconv

[thompson-tomo]

Is your feature request related to a problem? Please describe

I want the detector to be following semconv attribute namimg

Describe the solution you'd like to see

The github detector leverages attributes defined in semconv rather than custom attributes

Describe alternatives you've considered

N/a

Additional context

https://opentelemetry.io/docs/specs/semconv/registry/attributes/cicd/

https://opentelemetry.io/docs/specs/semconv/registry/attributes/vcs/