Refactor/octavia loadbalancer

[yahor-kurachkin]

What this PR does / why we need it:
Refactors pkg/openstack/loadbalancer.go for readability and maintainability with no functional changes — extracting helpers, decomposing large functions, standardizing error handling, and adding docs. Split into four reviewable phase commits; all existing tests pass.

Which issue this PR fixes(if applicable):
#3076

Special notes for reviewers:

• [phase1] extract helper functions — small helpers to remove duplication (serviceName, checkLoadBalancerActive, resolveLBConfig, setPreferredIPFamily, poolProtocol, listener-deletion helpers, isListenerOwnedByService).
• [phase2] decompose large functions — break up the mega-functions (ensureOctaviaLoadBalancer, checkService, ensureFloatingIP, createOctaviaLoadBalancer, ensureLoadBalancerDeleted, deleteLoadBalancer, ensureOctaviaListener/Pool, checkServiceUpdate) into focused helpers
• [phase3] standardize error handling — %w wrapping + errors.Is for sentinel checks, aligned error wording.
• [phase4] add godoc comments, group into sections, a Test_poolProtocol unit test, and minor readability polish.

I think this file will eventually need to be split into several smaller files, and the current section organization may help with that.

Release note:

NONE

[kubernetes-prow]

PR needs rebase.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[kubernetes-prow]

Hi @yahor-kurachkin. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[kubernetes-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign anguslees for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• pkg/openstack/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[yahor-kurachkin]

@kayrus I think it would be better if you reviewed this PR, since you have the most context around this task. I can reorganize the PR differently, for example by splitting it into smaller PRs. Let me know what would be easier for you to review.