Support non-local database

[karlcz]

We want to make sure webauthn can be used in web servers sharing the same non-local database, e.g. for a load-balancing scenario:

• Ensure that webauthn honors the database connection string in webauthn_config.json
• Ensure that the deploy process honors the configured database connection string
• Allow for renaming of the database so that several webauthn deployments could safely share one database cluster without interference
• Allow for renaming of the webauthn database role so that webauthn deployments sharing one database cluster can still have privilege isolation from one another
• Allow provider-specific "secret" storage within the database to reduce the amount of state and config provisioning needed for a load-balanced web server scenario.