Instance level Maven endpoint

A common Maven endpoint should be available at the instance level. This has a number of benefits, including:

• Easier interaction for users, with a single Maven URL containing of your packages
• Projects that depend upon the repository output of other sister projects is easier to manage, without having to worry about cross-project access tokens

Proposal

• packages endpoint is available at instance level: /api/v4/packages/maven

Open questions

• Access control for publishing into these repositories.
• All child projects get full read access?