Add "labels" type

[MichaelHinrichs]

What:
Add a contribution type for labeling issues and pull requests.
Aliases: label, labeling, adding labels, applying labels.

Why:
Because there was no type for it.

How:
By adding the type.

Checklist:

• Documentation N/A
• Ready to be merged
• Added myself to contributors table.
  Bot Usage

@all-contributors add @MichaelHinrichs for code.

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[MichaelHinrichs]

Hello?

[JoshuaKGoldberg]

Hi! Following up on this PR now that there's a maintenance team ramping up:

• I believe this is what the existing maintenance group is for, no? Without a compelling motivation to add an additional "subset" type for labels I'm not convinced this is something that should be added.
• If you (or anybody reading this) wants to advocate for the labels type, I'd recommend filing a new feature request issue -filling out those questions- to make the case for it