Travis migrations to GitHub actions

[consideRatio]

With no reply from Travis still regarding #351, @manics @betatim and I have got started on some migrations.

Reference example

I have worked to provide relevant comments in the GitHub Workflow defined in jupyterhub/jupyterhub#3246 to be of use as a reference example of how things work.

Tips

• Python setup / Node setup: use the setup-python and setup-node actions, they run in less than a second because of a smart cache in the base environment.
• SSH key setup: to setup a SSH key for pushes git repos etc or just secrets in general, see how it can be done here.
• LANG env var: GitHub Workflow's aren't UTF-8 friendly by default, you may need to set it explicitly to C.UTF-8 sometimes.

  env:
    # UTF-8 content may be interpreted as ascii and causes errors without this.
    LANG: C.UTF-8

• fail-fast: false: By setting jobs.<name>.strategy.fail-fast: false you avoid letting all variations of the job stop when one of them fail.
• Job run with different parameterization: by using jobs.<name>.strategy.matrix you can let a single job definition run multiple times using permutation of variables, or just use a list of predefined sets of combinations to include using jobs.<name>.strategy.matrix.include.
• if conditions: Both steps and jobs can have if conditions set on them. Example:

  steps:
    - name: Start a database server (${{ matrix.db }})
      if: ${{ matrix.db }}

• PyPI releases: see migrate from travis to github actions oauthenticator#383
• npm releases: see travis -> github actions configurable-http-proxy#275
• GitHub actions badge for README files: The Workflow name is case sensitive and is what its named within the file, not the file name itself, watch out!
  

  [![GitHub Workflow Status](https://img.shields.io/github/workflow/status/jupyterhub/chartpress/Test?logo=github)](https://github.com/jupyterhub/chartpress/actions)

• Run workflow button: By setting on.workflow_dispatch you can get a button to manually run a workflow.
  
• Colors: GitHub Workflow's make git, pytest, etc not realize colors are supported, so we need to explicitly do git --no-pager diff --color and pytest --color=yes for example when using those commands.
  This all relates to this issue: Not a tty actions/runner#241, which wasn't an issue in Travis CI
• edit and add more here

Repo migration overview

• Replace Travis with GitHub workflow zero-to-jupyterhub-k8s#1896 (Helm chart release)
• Migrate from travis to GitHub actions jupyterhub#3246
• travis -> github actions configurable-http-proxy#275 (npm release)
• [MRG] Add basic GitHub Actions workflow for testing binderhub#1209 (PyPI release)
• Migrate from travis to GitHub actions kubespawner#459 (PyPI release)
• migrate from travis to github actions oauthenticator#383 (PyPI release)
• Migrate from Travis CI to GitHub Actions chartpress#101 (PyPI release)
• Travis -> GitHub workflows traefik-proxy#113 (PyPI release)
• GitHub actions + drop py35 ltiauthenticator#33 (PyPI release)
• GitHub Actions migration jupyter-server-proxy#225 (PyPI release, npm release)
• Migrate Travis CI to GitHub actions # firstuseauthenticator#35 (PyPI release)
• Migrate Travis CI to GitHub actions dockerspawner#397 (PyPI release)
• https://github.com/jupyterhub/ldapauthenticator (PyPI release)
• https://github.com/jupyterhub/nbgitpuller (PyPI release)
• https://github.com/jupyterhub/repo2docker (PyPI release)
• https://github.com/jupyterhub/batchspawner
• https://github.com/jupyterhub/jupyter-rsession-proxy
• https://github.com/jupyterhub/hubshare
• https://github.com/jupyterhub/yarnspawner
• https://github.com/jupyterhub/kerberosauthenticator
• (because its archived) https://github.com/jupyterhub/jupyterlab-hub

I've added a pypi_password secret for all pypi packages in this list as the jupyterhub-bot PyPI user except for the jupyterhub repo.

[consideRatio]

GitHub actions provides seemingly unlimited parallell builds! Omg!

[consideRatio]

@minrk can you add jupyterhub-bot on PyPI as a maintainer of dockerspawner https://pypi.org/project/dockerspawner/?