Switch from Travis to GitHub Actions.

[jason-fox]

As I'm sure you are aware from the TSC minutes, it appears that Travis is transitioning towards a paid pricing model. It would be opportune for active FOSS Projects to migrate to use the integrated GitHub Actions. It looks like each GitHub account is safe until January, but then travis-ci.org goes read-only then the 100000 credits start counting down. There is no clarity over if/how to obtain more credits, and indeed if they can be obtained in a timely manner.

Background links

• https://www.jeffgeerling.com/blog/2020/travis-cis-new-pricing-plan-threw-wrench-my-open-source-works
• https://www.reddit.com/r/programming/comments/jou1k9/travis_cis_new_pricing_plan_threw_a_wrench_in_my/
• https://www.reddit.com/r/haskell/comments/jvbs49/psa_maintainers_should_think_about_migrating_off/
• https://www.reddit.com/r/programming/comments/jmwj9m/the_travis_ci_blog_the_new_pricing_model_for/

This PR sets up the equivalent GitHub Action CI to the old Travis Yaml and as a bonus, the Docker linting , JavaScript linting and Markdown linting are also working.

[jason-fox]

The result of a test run can be seen here: https://github.com/jason-fox/IoTagent-LoRaWAN/actions/runs/381429507

[jason-fox]

Wrong branch