MariaDB/MySQL DB Check

Currently the only way to monitor MariaDB/MySQL is to ping port 3306. This causes a problem, as these connections stay open. Eventually the DB server will block the requestor IP for too many connections. Now you could lift the connection limit on the DB and varying other variables but on large enviroments that doesnt scale well.

**Describe the solution you'd like**
Taking a leaf out of Uptime Kuma's book, allow us to directly query the DB and return a value from a table. If that suceeds then to DB is "Up", if that fails then mark as down.

**Describe alternatives you've considered**
Adjusting values on the DB server to accomdate the non closed connections caused by the ping. However, large enviroments this is not feasible.

**Additional context**
This is the only feature missing that Uptime Kuma had that we miss (we migrated to Checkmate recently). Allowing us to directly query the DB will allow the connection to close and prevent IP blocks getting created when the connections are left open by port checking.