PR #92816 - kvserver: lower score threshold for mvcc GC eligibility

[cockroach-teamcity]

Exalate commented:

Related PR: cockroachdb/cockroach#92816
Commit: cockroachdb/cockroach@b013c84

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Release note (performance improvement): GC score triggering mvcc GC run
is lowered. GC Score is ratio is computed from mvcc stats and uses ratio
of live objects and estimated garbage age to estimate collectability of
old data. Reduced score will trigger GC earlier lowering interval between
runs 3 times, giving 2 times reduced peak garbage usage at the expense
of 30% increase of wasteful data scanning on constantly updated data.

Jira Issue: DOC-6353