Replace Jenkins CI/CD with GitHub Actions CI/CD

[mblomdahl]

Initially brought up during review of PR #86, the current CI/CD via Jenkins is broken and needs a replacement to continue structured and robust maintenance of this repository.

Draft acceptance criterion:

• Document how to add the necessary NPM credentials to the repo, replacing the current NPM_TOKEN = credentials('mblomdahl_npm') secret in Jenkinsfile L#131
• Evaluate and propose alternative to the current code for generating unique build identifiers, Jenkinsfile L#11-L#67
• Building from the release/x.y.z branch should push a release candidate to NPM
• Building from the master branch should push a release to NPM

Ping @gleite-smsi FYI!

[carlba]

Nice Github Actions are cool :)

[mblomdahl]

Nice Github Actions are cool :)

It is... Need a React app? GitHub Actions have you covered! 😁 https://github.com/mkdevops-se/web-template-react