[patch] Add standalone Db2uCluster to Db2uInstance migration pipeline and CLI command

[jainyjoseph]

Description

This PR introduces a new standalone Tekton pipeline and CLI command for migrating Db2uCluster instances to Db2uInstance

Changes

New CLI command(mas db2ucluster-migration)

• New module: python/src/mas/cli/db2_migration/ is added
• Integration: Updated cli.py and main.py to register new command
• Shell wrapper: Enhanced image/cli/mascli/mas script to support new command

New Tekton Pipeline

• Pipeline definition: tekton/src/pipelines/mas-devops-db2-migration.yml.j2
  • Standalone pipeline for DB2 migration workflow
  • Configurable parameters for namespace, cluster name, and backup options
• Task updates: Enhanced tekton/src/tasks/dependencies/db2.yml.j2 with migration parameters
• Build integration: Updated tekton/generate-tekton-pipelines.yml to include new pipeline

Key features

• Interactive cluster detection and selection
• Pre-migration backup support (configurable)
• Single-outage migration workflow
• Comprehensive parameter validation and user confirmation

Test results

You can refer test results in JIRA MASCORE-11096

Refer : ibm-mas/ansible-devops#2337
ibm-mas/python-devops#405