Make baseUrl configurable for Github

### Description

Github Enterprise has the possibility to run it under a custom URL.

### Possible solution

OctoKit has a baseUrl field which should be configurable. Default should be github.com

https://github.com/octokit/octokit.js/blob/main/README.md

https://github.com/kubero-dev/kubero/blob/main/server/src/git/github.ts#L15 

### Alternatives

-

### Additional information

_No response_