Add labels option

[jabranr]

Resolves #409

[peter-evans]

Hi @jabranr

Thank you for this contribution!

For consistency, I would love if this feature could be implemented in same way that labels are handled in create-pull-request.

• Use utils.getInputAsArray()
• Use the same wording for the description.

[peter-evans]

Let me merge this to a feature branch so I can make some minor adjustments. Then I'll merge it to main with your contributions.

[peter-evans]

Released as v2.2.0 / v2.

Note that I removed the functionality to remove all labels when no labels are specified because it's not backwards compatible behaviour. There could be users that apply labels to an issue and want to keep them when the issue is closed via this action. The labels input currently allows two modes, an empty string means "do nothing," and any content means "replace labels on the issue with the specified content."

Thank you!

[jabranr]

@peter-evans Thank you for picking it up and moving it forward. Apologies that I become quite busy so couldn't find time to return to this any sooner.