Fix deleting connections and applications and customers

[albertyfwu]

we no longer cascade on deletion of connections, because we want to force usage of syncService.deleteSync(id), so that we capture a task to clean up corresponding Temporal syncs.

We should implement the delete to clean the syncs up.

[albertyfwu]

this is addressed for connections but not yet applications

[albertyfwu]

not going to support this type of cascade delete. instead, return a better error to user to disallow deleting unless all associated connections are deleted