add action outputs

[caioaao]

Description:
Add two outputs to the action: labels and removed-labels.

Related issue:
Closes #408 (previous PR that didn't include labels-to-remove)
Closes #60

Check list:

• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

[MaksimZhukov]

Hello @caioaao ! Thank you for the PR!
We are going to accept #60. It adds the all-labels output which is very useful because the github context contains a set of labels that are only available at the time the event is triggered, changes made during the workflow run won't show up there.
Could you please describe a use case for the removed-labels output?

[caioaao]

Hi @MaksimZhukov ! Sounds good. I didn't have any specific use-case in mind, just added it for completeness sake and I think having the all-labels output already fulfills my needs too :) . Since the other PR seems to be moving forward, I'll close this one. Thanks! 👋