Switch from Travis to GitHub Actions

[joewiz]

Adapted from documentation app - another maven/npm hybrid:

• https://github.com/eXist-db/documentation/blob/master/.github/workflows/ci.yml (Move Travis CI to GitHub Actions documentation#597)
• https://github.com/eXist-db/documentation/blob/master/pom.xml (added Github Release Plugin and documentation documentation#644)

[joewiz]

I seem to recall that the important CI runs here ("push") are passing - and that the failing ones ("pull_request") won't matter once the PR is merged.