Allow Workspace Identities as an authentication method for Fabric SQL Databases

Currently the only method of authentication in Fabric pipeline connections to Fabric SQL databases is using OAUTH2, meaning that the credentials of a specific user need to be used (with all the attendant issues around user/credential expiry).
By allowing the option of workspace identity for authentication, no user creds would be needed.  Obviously correct access controls would need to be defined, but that's standard SQL Server maintenance.