PR #96128 - kvserver: introduce cpu load based splits

[cockroach-teamcity]

Exalate commented:

Related PR: cockroachdb/cockroach#96128
Commit: cockroachdb/cockroach@408e227
Fixes: cockroachdb/cockroach#95377 cockroachdb/cockroach#83519 cockroachdb/cockroach#95377

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Release note (ops change): Load based splitter now supports using request
cpu usage to split ranges. This is introduced with the previous cluster
setting kv.allocator.load_based_rebalancing.objective, which when set
to cpu, will use request cpu usage. The threshold above which
CPU usage of a range is considered for splitting is defined in the
cluster setting kv.range_split.load_cpu_threshold, which has a default
value of 250ms.

Jira Issue: DOC-6922