[REQ] Add git *flags* in the mantra config file

[mhatzl]

Is your feature request related to other issues/PRs?

no

Describe the solution you'd like

Provide git flags similar to $inherit as possible value for certain product settings.

For example:

• base should take the current git branch or HEAD commit sha with e.g. flags $git-branch or $git-commit
• version should try to resolve the differences to the latest git tag (with dirty flags added in case of changes since tag) e.g. $git-tag
• repository might be possible to take the main git origin $git-origin

Describe alternatives you've considered

externally modifying the config file or using envs,
but this makes everything unnecessarily complex.

Additional context

[mhatzl]

those git flags may also be allowed at the top level of the mantra config