K8SPG-1104: update custom-extensions e2e test

[pooknull]

https://perconadev.atlassian.net/browse/K8SPG-1104

DESCRIPTION

This PR replaces pg_cron with pg_stat_kcache extension for custom-extensions test

CHECKLIST

Jira

• Is the Jira ticket created and referenced properly?
• Does the Jira ticket have the proper statuses for documentation (Needs Doc) and QA (Needs QA)?
• Does the Jira ticket link to the proper milestone (Fix Version field)?

Tests

• Is an E2E test/test case added for the new feature/change?
• Are unit tests added where appropriate?

Config/Logging/Testability

• Are all needed new/changed options added to default YAML files?
• Are all needed new/changed options added to the Helm Chart?
• Did we add proper logging messages for operator actions?
• Did we ensure compatibility with the previous version or cluster upgrade process?
• Does the change support oldest and newest supported PG version?
• Does the change support oldest and newest supported Kubernetes version?

[JNKPercona]

Test Name	Result	Time
backup-enable-disable	passed	00:19:33
builtin-extensions	passed	00:08:05
custom-extensions	passed	00:15:09
cert-manager-tls	passed	00:10:38
custom-envs	passed	00:20:28
custom-tls	passed	00:06:49
database-init-sql	passed	00:02:25
demand-backup	passed	00:26:42
demand-backup-offline-snapshot	passed	00:13:47
dynamic-configuration	passed	00:03:51
finalizers	passed	00:04:03
init-deploy	passed	00:03:09
huge-pages	passed	00:02:56
major-upgrade-14-to-15	passed	00:13:25
major-upgrade-15-to-16	passed	00:11:57
major-upgrade-16-to-17	passed	00:14:47
major-upgrade-17-to-18	passed	00:13:01
ldap	passed	00:05:51
ldap-tls	passed	00:07:56
monitoring	passed	00:08:51
monitoring-pmm3	passed	00:08:41
one-pod	passed	00:06:47
operator-self-healing	passed	00:10:50
pgbouncer-mtls	passed	00:05:02
pitr	passed	00:14:18
scaling	passed	00:06:17
scheduled-backup	passed	00:34:51
self-healing	passed	00:09:03
sidecars	passed	00:02:43
standby-pgbackrest	passed	00:19:14
standby-streaming	passed	00:13:36
start-from-backup	passed	00:12:30
tablespaces	passed	00:07:07
telemetry-transfer	passed	00:04:40
upgrade-consistency	passed	00:07:40
upgrade-minor	passed	00:07:40
users	passed	00:05:02
migration-from-crunchy-standby	passed	00:21:21
migration-from-crunchy-pv	passed	00:08:57
migration-from-crunchy-backup-restore	passed	00:16:01

Summary	Value
Tests Run	40/40
Job Duration	02:31:33
Total Test Time	07:16:03

commit: e684267
image: perconalab/percona-postgresql-operator:PR-1697-e684267e6