New GitHub Plugin

[Manas23601]

What does this PR change?

• Adds plugin for github

How will this PR impact users?

• They can get github billing reports for github-actions, github-packages and github-storage

Does this PR address any GitHub or Zendesk issues?

• Github Billing and Usage #42

How was this PR tested?

• Not tested, yet, need organisation access key.

Does this PR require changes to documentation?

• Will need documentation on how to use and so on

[Manas23601]

@cliffcolvin, I need your thoughts on the rest-api for github billing. enhanced-billing, although not straightforward (in the sense of time windows with start and end options), does have an option to fetch billing metrics for a time interval. The problem here is there is support for the enhanced billing API in the GO SDK for GitHub.

We have two options:

1. Ditch the GitHub SDK and create our own structs and functions.
2. Contribute to the Go SDK to support the enhanced-billing functionalities.

Couple of questions:

1. Do we have to stick to plugins made by well-established communities like Google?
2. Should the API support billing for an organisation, user or both?