Include Cloud SQL database connectors

[dustin-decker]

Description

Adds database connectors to facilitate securely connecting to Cloud SQL with IAM and MTLS encryption. This is the easiest way to connect securely when running Dependency Track on GCP.

This includes Cloud SQL for Postgres, MySQL, and SQL Server.

https://github.com/GoogleCloudPlatform/cloud-sql-jdbc-socket-factory

This socket factory also adds to capability to connect to databases through unix sockets: https://github.com/GoogleCloudPlatform/cloud-sql-jdbc-socket-factory/blob/main/docs/jdbc-postgres.md#connection-via-unix-sockets

Addressed Issue

Closes #2650

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have added corresponding update logic
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[syalioune]

Wouldn't using Cloud SQL Auth Proxy be easier and less invasive for Dependency Track ? I don't know much about Cloud Run but for GKE it's quite straightforward (c.f https://cloud.google.com/sql/docs/mysql/connect-kubernetes-engine)

For maintenance sake, I think it shouldn't be Dependency Track responsibility to adapt to each and every deployment context (i.e. embed connectors for all possible public or private cloud).

[dustin-decker]

When running in a serverless environment such as Cloud Run there isn't an opportunity to run a side car like Cloud SQL Auth Proxy. But Cloud Run will make a unix socket available to connect to the database. A socket factory must be provided to connect to a unix socket as well. The socket factory in this PR can connect to both a unix socket and directly to the Cloud SQL instance.

https://github.com/GoogleCloudPlatform/cloud-sql-jdbc-socket-factory/blob/main/docs/jdbc-postgres.md#connection-via-unix-sockets

[nscuro]

Including the connectors is fine I think, as we want users to be able to run DT in various cloud settings. They don't interfere with any of the JDBC connectors, so they're not that invasive.

The major downside here is that we as maintainers will not be able to test whether these connectors work, and continue to work.