Add support for gitlab private repositories

[dasJ]

We kind of need this

[piegamesde]

Thank you, this looks pretty solid. Some quite notes:

• If the token has other uses other than private repositories (e.g. rate limiting), maybe a more generic name like auth_token or access_token would be preferable?
• How does the Nix side fetcher handle this? That change is missing from the PR
• I'll have to think about that some more, but it's pretty likely that this will require incrementing the format version again.

[dasJ]

• I actually had the field named access_token during development but I changed it to private_token. This is the relevant docs so if you want me to change it, I will
• The fetcher handles this as the ?private_token=… is appended to the URL
• I think the format should be backwards compatible as older npins versions just ignore the field

[piegamesde]

Since the added field may be required for private repositories to successfully fetch, older versions can't really ignore it. Therefore, I'm in favor of incrementing the format version.

[andir]

Please don't forget to add unit tests for the new fields/logic in the GitLab case. We shouldn't let those fall behind. Especially if we can't (easily) have an integration tests those should be present.

[dasJ]

Added tests, added more docs, added token via environment, bumped the version

[dasJ]

Andi mach release

[piegamesde]

piegames macht release