Add datastore flavor association support

Trove currently supports associating flavors with datastore versions through trove-manage, which requires direct access to the Trove control plane. This is unsuitable for deployments where datastore version maintenance is automated through API workflows or control plane access is restricted.

Add –flavors and –remove-flavors options to the openstack datastore version set command. These options allow operators to manage datastore version flavor associations through the Trove management API.