chore: initial GitHub releases action

[Salakar]

Description

This GitHub action creates (or updates) the latest release for each extension, triggered only on push to master only.

• Finds all Extensions (directories containing extension.yaml file)
• For each Extension:
  • Read current Extension version from yaml file
  • Read changes for the version from the extensions CHANGELOG.md
  • Query GitHub API for firebase/extensions repo and checks if release exists already:
    • EXISTS: update it release body (allows changes made in CHANGELOG.md after a release to be automatically reflected in the relevant release)
    • DOES_NOT_EXIST: create a new GitHub release & tag

Notes:

• GITHUB_TOKEN secret automatically provided by GitHub actions
• GITHUB_REPOSITORY is a default environment variable

Testing

Script output:

Generated releases:

[codecov-io]

Codecov Report

Merging #272 into next will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             next     #272   +/-   ##
=======================================
  Coverage   40.48%   40.48%           
=======================================
  Files          20       20           
  Lines         625      625           
  Branches       81       81           
=======================================
  Hits          253      253           
  Misses        370      370           
  Partials        2        2           

[russellwheatley]

LGTM