Support mysql/postgres connection to passwordless services in AWS/Azure/GCP

[ciarancourtney]

Warpgate could act as a bastion/proxy to external databases that only allow token based auth, which is not always possible/easy to add support for in a service that only support static DB connection DSNs

I believe Teleport support this, although its unclear if they can expose a static DB DSN https://goteleport.com/docs/enroll-resources/database-access/enroll-azure-databases/azure-postgres-mysql/