feat(databases): Manage database servers as resources

[nfebe]

Database operations currently require the client to resend a complete connection, including its password, for every request. Model database servers as durable resources so authorized users can provision databases and receive usable connection details without storing administrator credentials in the browser.

Checklist

• Register, update, list, test, and remove database servers through the API
• Store server credentials with the existing protected credential facilities
• Scope server and database operations through database permissions
• Create a database and optional dedicated user on a selected server
• Return internal connection fields and a connection URL when credentials are created
• Reveal generated credentials once and redact them from later responses
• Support PostgreSQL, MySQL, and MariaDB
• Cover the resource lifecycle through HTTP tests

Related

• feat: Add endpoints for provisioning infrastructure; mariadb, mysql, redis, cerbot nginx etc #107
• feat: Allow configuration of mulitple shared resources #115