add workflow to copy doc issues to docs-content

[skedwards88]

Following discussion between the docs team and API team, we decided to copy docs-related rest-api-description issues to the docs-content repo so that the issue can be triaged appropriately. (We create a copy instead of transferring so that the issue does not disappear for the contributor.)

This PR adds a workflow that will create a copy of an issue when the documentation label is added and comment on the new issue about where the issue came from, the priority, and what to do when resolving the issue.

Note: The workflow references a secret called PERSONAL_ACCESS_TOKEN. A PAT that the ability to read issues in the rest-api-description repo and write issues in the docs-content repo should be stored as a secret in the rest-api-description repo. The workflow should be updated to reference this new secret.