K8SPG-175: add `standby` test

[pooknull]

https://jira.percona.com/browse/K8SPG-175

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 the manifests (crd/bundle) regenerated if needed?
• [ ] 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	Status
demand-backup	passed
init-deploy	passed
monitoring	passed
operator-self-healing	passed
scaling	passed
scheduled-backup	passed
self-healing	passed
standby	failure
start-from-backup	passed
telemetry-transfer	passed
users	passed
We run 11 out of 11

commit: https://github.com/percona/percona-postgresql-operator/pull/568/commits/f9f8255daa0ead8ca0f0269819cd605526fc0451 image: perconalab/percona-postgresql-operator:PR-568-f9f8255da