K8SPG-518: Don't set latest restorable time if it's earlier than backup start

[egegunes]

CHANGE DESCRIPTION

Problem:
We were setting latest restorable time to backup even though there are no new transactions committed to database.

Solution:
Check if latest restorable time is earlier than backup start timestamp and don't set it to backup if it's.

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?
• 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
custom-extensions	passed
demand-backup	passed
init-deploy	passed
major-upgrade	passed
monitoring	passed
one-pod	passed
operator-self-healing	passed
pitr	passed
scaling	passed
scheduled-backup	passed
self-healing	passed
start-from-backup	passed
tablespaces	passed
telemetry-transfer	passed
upgrade-consistency	passed
upgrade-minor	passed
users	passed
We run 17 out of 17

commit: b4cc234
image: perconalab/percona-postgresql-operator:PR-817-b4cc23420