New GitHub Team with triage access

As proposed by @eerovaher in the 2024-09-05 dev telecon. I have agreed to create this issue as a result of that discussion and will put this issue in the CoCo tag-up agenda on 2024-09-16 for further discussions.

Astropy Project or its stakeholders now hire contractors/staff with dedicated Astropy development time (e.g., @neutrinoceros and @jeffjennings). These hires may or may not have a named role in the Project and usually are only paid for a termed position. In such situation, it would be desirable to have a GitHub Team to give these developers triage access so they can label and milestone their PRs as needed (labels also drive the CI), instead of waiting for a maintainer to do it for them.

At the time of writing, there is no existing team for `astropy` (the core library) with only triage access. The permission scheme seems to jump from read-only (for assignments) straight to write access (maintainers).

Desired outcome: A new GitHub Team called ~`astropy-paid-contractors`~ `astropy-triage` with only triage access to `astropy` repository.

Start by reviewing the 2024-09-05 dev telecon discussion and the CoCo tag-up agenda referenced in the issue. Confirm the desired team name is astropy-triage, then create it with triage-only access to the astropy repository; done means the team exists with that permission and no write access.

Written by the indexing model from the issue text.