Add kubevirt-datamover plugin support to DPA

[Joeavaikath]

Why the changes were made

Adds support for the kubevirt-datamover plugin as a new default plugin option in the DataProtectionApplication CRD. This plugin enables data movement capabilities for KubeVirt virtual machines during backup and restore operations.

Changes include:

• Add DefaultPluginKubeVirtDataMover constant to DefaultPlugin enum
• Add KubeVirtDatamoverImageKey to unsupportedOverrides configuration
• Add plugin image constant and name mapping in pkg/common
• Add credentials and image retrieval logic in pkg/credentials
• Update CRD validation to accept 'kubevirt-datamover' plugin value
• Update bundle manifests with new plugin enum value

Users can now specify 'kubevirt-datamover' in the DPA spec:
spec:
configuration:
velero:
defaultPlugins:
- kubevirt-datamover

This will close #2065

How to test the changes made

Once the kubevirt-datamover image exists to be tested, supplying the kubevirt-datamover in defaultPlugins should work

[coderabbitai]

Walkthrough

Adds support for a new KubeVirt data mover plugin variant to OADP by introducing plugin constants, extending CRD schemas to include the plugin identifier in default plugins and unsupported image overrides, and configuring plugin-specific metadata.

Changes

Cohort / File(s)	Summary
API Type Definitions api/v1alpha1/dataprotectionapplication_types.go	Adds DefaultPluginKubeVirtDataMover constant ("kubevirt-datamover") and KubeVirtDatamoverImageKey constant ("kubevirtDatamoverPluginImageFqin") to support plugin enumeration and image override configuration.
CRD Manifest & Bases bundle/manifests/oadp.openshift.io_dataprotectionapplications.yaml config/crd/bases/oadp.openshift.io_dataprotectionapplications.yaml	Extends CRD validation schemas by adding "kubevirt-datamover" to defaultPlugins array and "kubevirtDatamoverPluginImageFqin" to unsupportedOverrides map in both manifest and base configurations.
Plugin Configuration pkg/common/common.go pkg/credentials/credentials.go	Adds KubeVirtDatamoverPluginImage and KubeVirtDatamoverPlugin constants in common package; extends PluginSpecificFields map with KubeVirt datamover configuration and updates GetPluginImage switch-case to handle the new plugin variant.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Assessment against linked issues

Objective	Addressed	Explanation
DPA changes for KubeVirt data mover plugin support [#2065]	✅
Plugin new fields and configuration [#2065]	✅
Unsupported overrides for controller plugins [#2065]	✅

✨ Finishing touches

• 📝 Generate docstrings

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[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Joeavaikath
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[openshift-ci]

@Joeavaikath: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/4.21-e2e-test-cli-aws	9a94818	link	false	/test 4.21-e2e-test-cli-aws

Full PR test history. Your PR dashboard.

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