Add Project Access Tokens

[bensofficial]

For further development within the Artemis project we need project access tokens. Therefore, we implemented the corresponding feature.

This PR adds the methods to interact with the project access tokens API provided by GitLab.

I have tested the newly introduced methods with GitLab version 13.10.

If you have questions, please let us know.

Closes #693

[bensofficial]

@jmini Thank you for your feedback 🙏 . I implemented your suggestions.

[bensofficial]

Regarding the failing test case: Some of the API endpoints have been added in GitLab release 14.10 and 16.0 (https://gitlab.com/gitlab-org/gitlab/-/merge_requests/82714 or https://gitlab.com/gitlab-org/gitlab/-/merge_requests/120436). As the tests currently run against GitLab 13.9 the newly added test cases will fail for an obvious reason.
Maybe I should disable the tests until the version of the GitLab instance is updated in the pom.xml. What do you think @jmini?

[jmini]

As the tests currently run against GitLab 13.9 the newly added test cases will fail for an obvious reason.
Maybe I should disable the tests until the version of the GitLab instance is updated in the pom.xml.

Yes I think we already did something like that in #963 just adding a NOTE.

There is an idea to switch the GitLab instance that used in the integration tests #925, but I don't know if there are any progress.
Once we have a more recent version, we can enable back those tests.

[bensofficial]

Great. I will add it tomorrow, and then the PR is good to go 😄

[bensofficial]

@jmini I have now commented out the affected lines. Everything works now 👍

[jmini]

Merged, thank you very much for this contribution! 🎉