K8SPG-332: don't pause cluster while running backup

[pooknull]

https://jira.percona.com/browse/K8SPG-332

DESCRIPTION

Problem:
If we pause the cluster during a running backup, the backup will continue to run while the cluster is paused.

Cause:
We are not checking whether the cluster is paused when starting the backup or if the backup is running when attempting to pause it.

Solution:
We should check it and wait until the backup is finished if there is already a running backup, or until the cluster is unpaused if we're trying to pause the cluster.

This PR also fixes https://jira.percona.com/browse/K8SPG-279

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
start-from-backup	passed
telemetry-transfer	passed
users	passed
We run 10 out of 10

commit: c8946c0
image: perconalab/percona-postgresql-operator:PR-545-c8946c083