Refactor auth modes dropping DRILL_PROCESS and allowing credential providers everywhere

Remove the abstract CredentialedStoragePluginConfig (formerly AbstractSecuredStoragePluginConfig) class and promote the credential provider members to the parent StoragePluginConfig. Since having a credential provider provider is optional, there is no harm in giving the capability to every plugin's config.

Drop the DRILL_PROCESS auth mode since this case is adequately covered by using SHARED_USER with no credentials specified.

Bug fix. In storage-jdbc and when there are no JDBC credentials for the query user, only forgo an attempt to connect if the auth mode is USER_TRANSLATION. If it is SHARED_USER, proceed with an attempt to connect (examples of this case are unsecured DBs and BigQuery which requires OAuth tokens in the JDBC URL instead of a JDBC username and password).