Description:
Currently, it is possible to generate a settings.xml that contains exactly one server section with GH credentials.
Instead, it should be possible to generate multiple server sections with GH credentials.

Justification:
When a project depends on multiple other projects that each use GitHub packages, then it needs to include a repository declaration for each of these. However, these repository declarations cannot all use the same ID github because the IDs must be unique. So in order to be able to draw in dependencies from multiple GitHub packages repositories, it must be possible to generate multiple server sections, one for each of the GitHub packages repositories.