Respect share backup "use data manager" boolean in data manager

support for creating backups of Manila shares was added in https://review.opendev.org/c/openstack/manila/+/343980

This included a base backup driver class '/manila/data/backup_driver.py` containing a boolean flag `self.use_data_manager` to dictate whether the data manager 'manila/data/manager.py' should take authority for performing and handling backups, or if this should be deferred to the driver itself.

At current, the data manager does not take this this boolean flag into consideration, this blueprint proposes to add simple checks to the data manager functions related to performing backups, namely:

`_run_backup`
`delete_backup`
`_run_restore`

while excluding:
`create_backup`
`create_restore`

such that the former set respect this boolean flag if used, allowing a driver implemented from the base class 'manila/data/backup_driver.py' and loaded by the data manager to take the impetus for backups into its own scope.

Additionally, support for this boolean in the following periodic task functions:
`create_backup_continue`
`restore_backup_continue`

Should be handled in a seperate blueprint, along with work to allow for the current data_manager `get_progress` function (that both utilise to establish the progress of a given restore or backup action) to be carried out from the driver (base class changes)