Feature/reserve identifier with new issue url

[dxL1nus]

Closes #99,
closes #62,
closes #53,
closes #104,
closes #55,
closes #100,
closes #101,
closes #125

This PR is a massive one, but needed as most of the functionality is based upon each other, although there are a number of features addressed here.

Features that come with this PR:

• Reserving identifiers with a GitHub New Issue URL Link
• Linking manually created GtiHub Issue to the Certificate Identifier in OJS Submission
• Update the information in the GitHub Issue (on metadata form save)
• Delete concept of Venue Type & Venue Name as Labels (instead all labels in one central Dropdown)
  • Labels are cached / saved in the OJS DB (and only fetched from the API, when they are older than 6 hours)

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❗ I want to include a setting in the settings form for a feature which is only introduced with this PR here (#101).

[dxL1nus]

so far this is a draft, because all parts are finished except for Issue #100. @nuest do we need this issue here in this stage already or can it be introduced at a later stage, so we can merge this PR. What do you think?

[dxL1nus]

Plus it is a draft still, because I need to fix the unit tests here, which so far don't work

[dxL1nus]

Plus it is a draft still, because I need to fix the unit tests here, which so far don't work

So far I fixed nearly every unit test apart from two, as I am not quite sure how to fix them yet (I will look into it further).

I will definitely also need to add some new unit tests as well.

[dxL1nus]

This branch now got fully rebased and is ready for review.

!!!! Though a merge should only happen after #108 !!!!

@nuest

[dxL1nus]

@nuest you may now review this PR, as every test works again and the rebase to the current version of main is also done