Fix Azure SLB support for multiple backend pools

[feiskyer]

Azure VM and vmssVM support multiple backend pools for the same SLB, but
not for different LBs.

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:

SLB backend pools are empty if outbound rules are defined in a separate backend pool.

This is because, although we added the check for not adding the backend pools from different LBs, the lbName is not checked.

This PR fixes the issue by also checking the LB name.

Which issue(s) this PR fixes:

Fixes #76687

Special notes for your reviewer:

Should cherry pick to old releases.

Does this PR introduce a user-facing change?:

Ensure the backend pools are set correctly for Azure SLB with multiple backend pools (e.g. outbound rules)

/kind bug
/sig azure
/priority critial-urgent

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: feiskyer

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[feiskyer]

/priority critical-urgent
/assign @andyzhangx @khenidak

[feiskyer]

/test pull-kubernetes-e2e-aks-engine-azure

[feiskyer]

/retest

[andyzhangx]

is it possible to combine the code change (use a standalone function?) under vmas and vmss, it's quite similar:

			newBackendPoolsIDs := make([]string, 0, len(newBackendPools))
			for _, pool := range newBackendPools {				for _, pool := range newBackendPools {
				backendPool := *pool.ID					if pool.ID != nil {
				matches := backendPoolIDRE.FindStringSubmatch(backendPool)						newBackendPoolsIDs = append(newBackendPoolsIDs, *pool.ID)
				if len(matches) == 2 {	
					lbName := matches[1]	
					if strings.HasSuffix(lbName, InternalLoadBalancerNameSuffix) == isInternal {	
						klog.V(4).Infof("Node %q has already been added to LB %q, omit adding it to a new one", nodeName, lbName)	
						return nil	
					}	
				}					}
			}				}
			isSameLB, oldLBName, err := isBackendPoolOnSameLB(backendPoolID, newBackendPoolsIDs)
			if err != nil {
				return err
			}
			if !isSameLB {
				klog.V(4).Infof("Node %q has already been added to LB %q, omit adding it to a new one", nodeName, oldLBName)
				return nil
			}

[feiskyer]

is it possible to combine the code change (use a standalone function?) under vmas and vmss, it's quite similar

that's already done in func isBackendPoolOnSameLB(). The other parts couldn't be combined because of different data struct.

[feiskyer]

@andyzhangx Addressed comments. PTAL

[feiskyer]

/retest

[andyzhangx]

/lgtm