Create GitHub Action for creating and releasing videos

Re-ticketed from: https://github.com/mifi/editly/issues/62#issuecomment-740241101

The proposal is to have a github action (or just a workflow template) to help FOSS projects keep a json config file in their project, and have videos generated automatically by GitHub Actions. This would allow supportive video resources to be created with very little maintenance burden on project owners.

The thought is that it might help projects to make it simple for them to generate videos. This could happen according to various triggers:

• on changes to json config file or source material
• on tagging (to generate a new video for docs on official release)
• each commit (assuming e2e test specs are recorded as video content, see below)

Resources

• Cypress GitHub Action: https://github.com/cypress-io/github-action
  • this action also updates videos as assets, so could use it as reference
  • perhaps there's a way to have Cypress also generate "walkthrough" videos for projects, which editly could assemble into supportive videos showcasing project behavior. I'm sure there's a pattern here worth thinking about, but i don't have a full view
• https://github.com/actions/upload-artifact
  • how cypress action recommends uploading

To Do

• get editly working in docker (#96)
• get simple MVP GitHub Action build working in new repo: https://github.com/patcon/editly-videos
• get upload-artifact action working
• Add simple cypress run workflow, and incorporate generated video into demo
• stretch: create a github action repo
• stretch: integrate GitHub Packages to store docker images (so no need to rebuild)

Start with the MVP workflow in the patcon/editly-videos repository and review the Cypress GitHub Action and actions/upload-artifact references. Define the remaining scope around adding a Cypress run workflow and incorporating its generated video into the demo; the stretch goals cover a standalone action repository and GitHub Packages Docker images.