K8SPXC-1688 support adding existing pvcs to pxc instances

[gkech]

CHANGE DESCRIPTION

Problem:

Related Github issue: #2126

Adds support for mounting existing PersistentVolumeClaims (PVCs) to PXC, ProxySQL, and HAProxy pods using the new extraPVCs field. This allows users to attach pre-existing storage volumes to their database instances for use cases such as importing data, sharing configuration files, or accessing external datasets.

Important notes:

• Added new ExtraPVC type in pkg/apis/pxc/v1/pxc_types.go with fields:
  • name: Volume name reference
  • claimName: Name of existing PVC to mount
  • mountPath: Path inside container
  • subPath: Optional subpath within volume
  • readOnly: Optional read-only flag
• extraPVCs field was added to PodSpec (PXC, ProxySQL, HAProxy)
• new e2e test to verify the functionality

Helm chart PR: percona/percona-helm-charts#719

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

[egegunes]

@gkech please add description to the PR

[JNKPercona]

Test Name	Result	Time
auto-tuning-8-0	passed	00:00:00
allocator-8-0	passed	00:00:00
backup-storage-tls-8-0	passed	00:00:00
cross-site-8-0	passed	00:00:00
custom-users-8-0	passed	00:00:00
demand-backup-cloud-8-0	passed	00:00:00
demand-backup-encrypted-with-tls-8-0	passed	00:00:00
demand-backup-encrypted-with-tls-8-4	passed	00:00:00
demand-backup-8-0	passed	00:00:00
demand-backup-flow-control-8-0	passed	00:00:00
demand-backup-parallel-8-0	passed	00:00:00
demand-backup-without-passwords-8-0	passed	00:00:00
extra-pvc-8-0	passed	00:00:00
haproxy-5-7	passed	00:00:00
haproxy-8-0	passed	00:00:00
init-deploy-5-7	passed	00:00:00
init-deploy-8-0	passed	00:00:00
limits-8-0	passed	00:00:00
monitoring-2-0-8-0	passed	00:00:00
monitoring-pmm3-8-0	passed	00:00:00
one-pod-5-7	passed	00:00:00
one-pod-8-0	passed	00:00:00
pitr-8-0	passed	00:00:00
pitr-gap-errors-8-0	passed	00:00:00
proxy-protocol-8-0	passed	00:00:00
proxy-switch-8-0	passed	00:00:00
proxysql-sidecar-res-limits-8-0	passed	00:00:00
proxysql-scheduler-8-0	passed	00:00:00
pvc-resize-5-7	passed	00:00:00
pvc-resize-8-0	passed	00:00:00
recreate-8-0	passed	00:00:00
restore-to-encrypted-cluster-8-0	passed	00:00:00
restore-to-encrypted-cluster-8-4	passed	00:00:00
scaling-proxysql-8-0	passed	00:00:00
scaling-8-0	passed	00:00:00
scheduled-backup-5-7	passed	00:00:00
scheduled-backup-8-0	passed	00:00:00
security-context-8-0	passed	00:00:00
smart-update1-8-0	passed	00:00:00
smart-update2-8-0	passed	00:00:00
storage-8-0	passed	00:00:00
tls-issue-cert-manager-ref-8-0	passed	00:00:00
tls-issue-cert-manager-8-0	passed	00:00:00
tls-issue-self-8-0	passed	00:00:00
upgrade-consistency-8-0	passed	00:00:00
upgrade-haproxy-5-7	passed	00:00:00
upgrade-haproxy-8-0	passed	00:00:00
upgrade-proxysql-5-7	passed	00:00:00
upgrade-proxysql-8-0	passed	00:00:00
users-5-7	passed	00:00:00
users-8-0	passed	00:00:00
validation-hook-8-0	passed	00:00:00

Summary	Value
Tests Run	52/52
Job Duration	00:07:09
Total Test Time	N/A

commit: ee0ffc9
image: perconalab/percona-xtradb-cluster-operator:PR-2276-ee0ffc97