[minor] Control Db2-channel version in operator catalog metadata

[jainyjoseph]

Description

Currently, the operator catalog metadata controls the Db2u operator version, but there is no mechanism to control the Db2 operand version (v11 vs v12) being installed. As a result, the Db2 operand version is hardcoded to v11 across the Ansible collection.

This PR introduces a new catalog-level parameter, db2_channel_default, which allows the catalog metadata to define the default Db2 operand version. The Ansible logic now consumes this value to determine whether Db2 v11 or v12 should be installed, instead of relying on hardcoded defaults.

Epic

JIRA 11097

What’s Changed

• Introduced db2_channel_default in the operator catalog metadata
• Python CLI now reads the Db2 default channel from the catalog instead of using a hardcoded value
• In non-dev mode, Db2 version selection is driven by catalog metadata
• Enables per-catalog control of Db2 operand version (v11 vs v12)
• Fix for User-provided db2_channel usage in non-dev mode

Benefits

• Enables catalog-driven control of Db2 operand version
• Eliminates hardcoded Db2 version logic in Ansible
• No manual intervention required to manage Db2 version selection
• Fully backward compatible with existing workflows

Testing Performed

DEV Mode

1. User sets db2_channel, catalog has db2_channel_default

   • Result: db2_channel is honored as per user input

2. User does not set db2_channel, catalog has db2_channel_default

   • Result: Falls back to catalog default channel

Non-DEV Mode

1. Catalog sets db2_channel_default (default v11), user sets db2_channel

   • Result: db2_channel is honored as per catalog

2. Catalog does not set db2_channel_default

   • Result: Falls back to v11 (existing behavior)

Additional Notes

All test evidence and logs have been attached to the corresponding JIRA story (11097).