[occm] Support `loadbalancer.openstack.org/flavor-name` instead of only `loadbalancer.openstack.org/flavor-id`

[Sinscerly]

Is this a BUG REPORT or FEATURE REQUEST?:

/kind feature

What happened:

Reading the documentation for the cloud-provider-openstack I found it is possible to specify a loadbalancer flavor by id, although it would be handy and simpeler if it is possible to also create one by using the flavor name (if no flavor-id is specified).

What you expected to happen:

That a loadbalancer flavor is selected based on the name when the annotation loadbalancer.openstack.org/flavor-name is used