PR #90789 - server: use a common logic for system log gc (1 of 2)

[cockroach-teamcity]

Exalate commented:

Related PR: cockroachdb/cockroach#90789
Commit: cockroachdb/cockroach@c7ce656

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Release note (ops change): The cluster settings
server.web_session.purge.period and
server.web_session.purge.max_deletions_per_cycle, which were
specific to the cleanup function for system.web_sessions, have been
replaced by server.log_gc.period and
server.log_gc.max_deletions_per_cycle which apply to the cleanup
function for system.eventlog, system.rangelog and
system.web_sessions equally.

Jira Issue: DOC-6211