K8SPG-913: Update versions for 2.8.1 release

[eleo007]

CHANGE DESCRIPTION

Problem:
Short explanation of the problem.

Cause:
Short explanation of the root cause of the issue if applicable.

Solution:
Short explanation of the solution we are providing with this PR.

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	00:06:16
custom-envs	passed	00:18:01
custom-extensions	passed	00:15:58
custom-tls	passed	00:05:29
database-init-sql	passed	00:02:20
demand-backup	passed	00:25:03
finalizers	passed	00:04:55
init-deploy	passed	00:03:00
monitoring	passed	00:07:37
monitoring-pmm3	passed	00:09:22
one-pod	passed	00:06:21
operator-self-healing	passed	00:08:08
pgvector-extension	passed	00:02:53
pitr	passed	00:12:19
scaling	passed	00:05:29
scheduled-backup	passed	00:26:46
self-healing	passed	00:09:24
sidecars	passed	00:02:47
start-from-backup	passed	00:10:56
tablespaces	passed	00:07:33
telemetry-transfer	passed	00:03:48
upgrade-consistency	passed	00:12:26
upgrade-minor	passed	00:05:26
users	passed	00:04:53

Summary	Value
Tests Run	24/24
Job Duration	01:36:15
Total Test Time	03:37:21

commit: c5338ba
image: perconalab/percona-postgresql-operator:PR-1382-c5338ba41