[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.

[k8s-ci-robot]

Hi @Lucasgranet. Thanks for your PR.

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[nicolaslacroux]

Hello,

If you have some time, would you mind reviewing this PR please?

Thank you,

[Lucasgranet]

Hello @kayrus

I've applied all your suggestions.

[k8s-ci-robot]

@Lucasgranet: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
openstack-cloud-csi-cinder-e2e-test	203ad01845f5249e76fb1e270a6487997b9d518f	link	true	/test openstack-cloud-csi-cinder-e2e-test

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes-sigs/prow](https://github.com/kubernetes-sigs/prow/issues/new?title=Prow%20issue:) repository. I understand the commands that are listed [here](https://go.k8s.io/bot-commands).

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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