release-25.2: sqlinstance: deduplicate live rows by rpcAddr

[blathers-crl]

Backport 1/1 commits from #169043 on behalf of @shubhamdhama.

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selectDistinctLiveRows was deduplicating live SQL instance rows by sqlAddr (the SQL advertise address). This was the wrong key: the SQL advertise address (--sql-advertise-addr) is allowed to be non-unique across nodes — Kubernetes deployments commonly point it at a regional service DNS shared by all pods in the region. Deduplication on sqlAddr silently collapsed distinct live instances down to one entry, breaking downstream consumers like DistSQL placement and execution-locality filtering.

Switch the dedup key to rpcAddr. RPC advertise addresses must be node-unique among live instances — gossip and KV peer dialing depend on this — so rpcAddr is the correct identity for the pod-restart race that motivates dedup in the first place (a SQL pod crashes and a new pod starts at the same rpcAddr with a fresh instance ID before the dead pod's session expires).

The wrong key was introduced when the RPC and SQL listen ports were split; before the split there was a single advertise address and the choice was unambiguous.

Resolves: #168991
Epic: CRDB-63207

Release note (bug fix): Fixed a bug where setting --advertise-sql-addr to the same value across multiple SQL instances — for example, in a Kubernetes deployment where all pods in a region share a regional service DNS name — caused distributed SQL query plans to place onto a single instance per region, and could cause changefeeds with execution_locality filters to fail with "no instances found matching locality filter".

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Release justification:

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