Replace or remove `KeywordLabeler`

[llucax]

The repository https://github.com/ZeWaka/KeywordLabeler is archived with a message saying the app/infra that runs it doesn't work anymore.

NOTE: This GitHub App is depreceated/inactive, since the infrastructure operating this is no longer functional, and you can easily accomplish this with just using GitHub Actions functionality.

So we need to find an alternative and/or remove it.