[occm] Support Octavia load balancing method via annotation

[Lucasgranet]

What this PR does / why we need it: Adds the ability to change the LB Algorithm of an Octavia using an annotation.

This PR brings a new annotation:

loadbalancer.openstack.org/lb-method: "" # Default value: the one defined in the OCCM configuration file

Special notes for reviewers: N/A

Release note:

[occm] Octavia - ability to change the load balancing method using an annotation.