Update to using GHA for CI

[rofinn]

1. Use GHA CI workflows
2. Remove gitlab-ci.yml
3. Update all badges and links to gitlab workflows
4. Updated docs make.jl file and Documenter version

I'm not sure if we need all these tests, but I guess we can change that in a separate PR? I'll add the MIT license in a separate PR.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@4529f7e). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main       #2   +/-   ##
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  Coverage        ?   91.04%           
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  Files           ?        3           
  Lines           ?       67           
  Branches        ?        0           
=======================================
  Hits            ?       61           
  Misses          ?        6           
  Partials        ?        0           

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