Contributing actions API

[worksofliam]

Signed-off-by: Liam Barry Allan [email protected]

Changes

Allow other extensions to register actions. Needs testing.

Closes #755.

Test list

• [ ] Local actions continue to work (validator changed)
• [ ] Command to add actions

Checklist

• [ ] have tested my change
• [x] updated relevant documentation
• [x] Remove any/all console.logs I added
• [x] eslint is not complaining
• [ ] have added myself to the contributors' list in CONTRIBUTING.md
• [x] for feature PRs: PR only includes one feature enhancement.