First time contributor label

### Description

Is there a way to filter PRs by first time contributors? It can help reviewers prioritize reviewing them which would give more encouragement to first time contributors (Their changes would be reviewed swiftly).

If not, maybe we can achieve this through Github workflows (`author_association`?). Happy to work on it if there is consensus.

Start by checking whether GitHub pull-request filters expose first-time contributors through author_association, then review whether a GitHub workflow can apply a corresponding label. Done means reviewers can identify or filter pull requests from first-time contributors, with the approach agreed by the project.

Written by the indexing model from the issue text.