Move fully away from GitLab

[jeggy]

I'm thinking we should remove our whole dependency to gitlab.com by removing our .gitlab-ci.yml and when finished with that we would update the https://apurebase.gitlab.io/arkenv/ website to just forward all requests to https://arkenv.io/

Some tasks I can think of:

• [ ] Create Code coverage badge via GitHub Actions [An idea how]
• [x] Make sure all links work on the new arkenv.io webiste
• [x] Change references in this GitHub repo to point to arkenv.io
• [x] Update generated POM files to use new arkenv.io website
• [x] Stop mirror settings on GitLab & Create 1 commit on GitLab that:
  • [ ] Will publish a new website, which only forwards the link directly over to the new site.
  • [ ] A small note in the README to say we are not using GitLab anymore and a link to this repo instead.