Create github actions to replace travis to test openapi etc.

[eri-trabiccolo]

.travis.yml containing the following:

jobs:
  include:
  - name: "Test OpenAPI Spec"
    language: node_js
    node_js: lts/*
    before_install:
    install:
      - npm ci
    script:
      - npm run test
  - stage: deploy
    language: node_js
    node_js: lts/*
    if: branch = trunk AND env(GH_TOKEN) IS present
    before_install:
    install:
      - npm ci
    script: npm run build:docs && npm run gh-pages

has been removed.
Those jobs should be replaced with gh actions.

[eri-trabiccolo]

The deploy is already there (running on the trunk branch only), we need to create the test action only I guess.