Backport of state: ensure that identical manual virtual IP updates result in not bumping the modify indexes into release/1.20.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #21909 to be assessed for backporting due to the inclusion of the label backport/1.20.

The below text is copied from the body of the original PR.

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Description

The consul-k8s endpoints controller issues catalog register and manual virtual ip updates without first checking to see if the updates would be effectively not changing anything. This is supposed to be reasonable because the state store functions do the check for a no-op update and should discard repeat updates so that downstream blocking queries watching one of the resources don't fire pointlessly (and CPU wastefully).

While this is true for the check/service/node catalog updates, it is not true for the "manual virtual ip" updates triggered by the PUT /v1/internal/service-virtual-ip. Forcing the connect injector pod to recycle while watching some lightly modified FSM code can show that a lot of updates are of the update list of ips from [A] to [A]. Immediately following this stray update you can see a lot of activity in proxycfg and xds packages waking up due to blocking queries triggered by this.

This PR skips updates that change nothing both:

• at the RPC layer before passing it to raft (ideally)
• if the write does make it through raft and get applied to the FSM (failsafe)

Testing & Reproduction steps

• Deployed a small 1-node cluster using consul-k8s + kind with 2 connect-enabled services
• Watched the server debug logs before/during/after recycling the connect injector pod.
• Before you could see the api PUTs immediately preceding proxycfg/xds activity.
• After you no longer see these as often.

PR Checklist

• updated test coverage
• [ ] external facing docs updated
• appropriate backport labels added
• not a security concern

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Overview of commits

• 36d5891 - 0754411 - 7e55ff3 - 90f8e8e - e86a5d9

[github-team-consul-core-pr-approver]

Auto approved Consul Bot automated PR