jsonnet: pass top level args providing build context

[sgotti]

We should pass some toplevel arguments to the jsonnet parser to ease the generation of the final config file without relying on build information currently only provided at runtime via environment variables:

• run ref type (branch, tag, pull request)
• git branch
• git tag
• git ref
• git commitsha

[m8nmueller]

You can assign me but it could take a few days until I find some time to do this.

[sgotti]

@MaxM123 Sorry but I already opened a PR with an initial implementation in #141 (would you like to review it?). If you want you can use it as a starting point for the implementation of the Starlark config language in #138 .

[m8nmueller]

Okay, great :). I can have a look at that but I will probably need some time to get to know Starlak and reorganize your configuration module (a little bit) to be able to check for which format to use. But I would be glad to work on that if you let me do that ;).
I will have a look at your PR but I guess, review isn't too necessary for that code if you wrote it.

[sgotti]

Implemented in #141