CLOUD-869 Fallback to merge-base if commit hash is invalid

[ptankov]

CHANGE DESCRIPTION

Problem:
Sometimes git diff --name-only xxxxx HEAD can result in:

fatal: bad object xxxxx

Cause:
The commit is from a different branch or repository.
or
The commit history has been rewritten (e.g., through a rebase or force-push).

Solution:
Validate the commit hash before running git diff and fallback to merge-base if the commit is invalid.

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?
• Are OpenShift compare files changed for E2E tests (compare/*-oc.yml)?

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 MongoDB version?
• Does the change support oldest and newest supported Kubernetes version?

[JNKPercona]

Test name	Status
arbiter	passed
balancer	passed
custom-replset-name	passed
custom-tls	passed
custom-users-roles	passed
custom-users-roles-sharded	passed
cross-site-sharded	passed
data-at-rest-encryption	passed
data-sharded	passed
demand-backup	passed
demand-backup-fs	passed
demand-backup-eks-credentials-irsa	passed
demand-backup-physical	passed
demand-backup-physical-sharded	passed
demand-backup-sharded	passed
expose-sharded	passed
ignore-labels-annotations	passed
init-deploy	passed
finalizer	passed
ldap	passed
ldap-tls	passed
limits	passed
liveness	passed
mongod-major-upgrade	passed
mongod-major-upgrade-sharded	passed
monitoring-2-0	passed
multi-cluster-service	passed
non-voting	passed
one-pod	passed
operator-self-healing-chaos	passed
pitr	passed
pitr-sharded	passed
pitr-physical	passed
preinit-updates	passed
pvc-resize	passed
recover-no-primary	passed
replset-overrides	passed
rs-shard-migration	passed
scaling	passed
scheduled-backup	passed
security-context	passed
self-healing-chaos	passed
service-per-pod	passed
serviceless-external-nodes	passed
smart-update	passed
split-horizon	passed
stable-resource-version	passed
storage	passed
tls-issue-cert-manager	passed
upgrade	passed
upgrade-consistency	passed
upgrade-consistency-sharded-tls	passed
upgrade-sharded	passed
users	passed
version-service	passed
We run 55 out of 55

commit: f3382fb
image: perconalab/percona-server-mongodb-operator:PR-1807-f3382fb1