Set up auto labeling of pull requests using github actions

[mithro]

A lot of the labels for a pull request could be automatically detected by the contents of the pull request.

Previously I have used the Probot Autolabler (and https://github.com/mithro/autolabeler) but the new way to do this seems to be with GitHub actions.

• https://github.com/actions/labeler
• https://github.com/marketplace/actions/auto-label-action
• https://github.com/Decathlon/pull-request-labeler-action
• https://github.com/banyan/auto-label
• https://github.com/TimonVS/pr-labeler-action
• https://github.com/marketplace/actions/autolabel
• https://github.com/marketplace/actions/label-approved-pull-requests
• https://github.community/t/pull-request-labeler/16605

[mithro]

The pull request at https://github.com/google/skywater-pdk/pull/38 change the GitHub labels to be managed by GitHub action workflow.

[mithro]

The top GitHub action called labeler has the following caveat;

Note that only pull requests being opened from the same repository can be labeled. This action will not currently work for pull requests from forks -- like is common in open source projects -- because the token for forked pull request workflows does not have write permissions.

Which means it currently can not be used by us, as this is how we do pull requests.

[mithro]

I ended up setting up Probot Autolabeler in #39

I opened #41 to track converting to a GitHub actions based flow in the future.