Improve register_check function

[angelina-momin]

In validate_codecheck_yml function the following should fail the validations:

1. The field "paper/ reference" in codecheck.yml contains extra text besides the link
2. The field "report" in codecheck.yml should be an actual link.
3. The field "ORCID ID" should only contain numbers and should be valid (there exists an ORCID page matching this ID and the author name)
4. The field "repository link" should be a valid URL

[angelina-momin]

@nuest feel free to add more points if I am missing anything

[nuest]

I can double check with the current specification what else we can check.

More of a question, because I might have badly phrased my intentions regarding the reference field: The current implementation fails if there is text in the field?

My idea was to have it check if it is a URL, then link, and if not, then there is no link but it does not fail. I think we want a bit flexibility here, to handle papers during review, for example, where we still want them to be present in the register but a DOI does not exist yet.