PCI-3118 github package refactoring

[aliculPix4D]

commit 1: github: pass the sink logger to github package

• enables logging from inside github package

commit 2:github: use 'http.Response.Header.Get(key)' to fetch the header

Advantages:

• http.Response.Header.Get(key) is an existing built-in method
• it handles canonicalization (go http server converts header keys into case-sensitive keys)
• caller doesn't need to check if the key exists or how many elements it has

Using http.Response.Header.Get(key) will be much more important when inspecting rate limit related headers.