Summary:
Disable running pg_cron jobs on a xCluster Automatic mode target universe. This enables the user to have pg_cron installed on a xCluster replicated databases with jobs that perform inserts. When a xCluster Switchover or failover operation happens the jobs are enabled on the new primary and blocked on the new target (if any).

Users can disable this feature by setting `cron.yb_enable_on_xcluster_target` to `true`.
Jira: DB-16180

Test Plan:
XClusterDDLReplicationTest.PgCron
XClusterDRTest.PgCron

Reviewers: jhe

Reviewed By: jhe

Subscribers: jason, yql, ybase

Differential Revision: https://phorge.dev.yugabyte.com/D45281