feat: support sharing the primary slb with multiple vmSets

[nilo19]

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

/kind feature

What this PR does / why we need it:

This PR enables multiple vmSets sharing the primary SLB. To do this, we need to:

1. turn on the multiple slbs mode;
2. store the vmSet names that share the primary SLB to a new cloud config nodePoolsWithoutDedicatedSLB (comma separated).

Note that when switching from dedicated slb to shared slb, the service frontend IP configs would be moved to the primary slb as well, even if there is a mode annotation that selects the original non-primary vmSet. This could cause service downtime for some local services.

Which issue(s) this PR fixes:

Fixes #549

Special notes for your reviewer:

Release note:

feat: support sharing the primary slb with multiple vmSets

[nilo19]

Want to prevent the 412 error here, even though the error won't break the logic because the retry wouldn't face the 412 error again.

[nilo19]

same here

[feiskyer]

move to defer and only set it to true when the following operations have succeeded.

[feiskyer]

and need pre-define the err above to catch the error inside defer function

[nilo19]

refactored

[feiskyer]

rename to shouldRemoveVMSetFromSLB()

[nilo19]

renamed

[feiskyer]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: feiskyer, nilo19

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