test: Add test environment variables

[nirs]

The test environment setup contains some hardcoded values like: https://github.com/RamenDR/ramen/blob/500a711a5428be5c63b96149b48013442a216c26/test/rook/start#L11

Change the way the values are kept so we can:

• Create same environment with different version of components (e.g. rook version) without editing the scripts
• Create different environment yamls using different configuration (e.g. external ceph cluster for metro-dr test environment)
• Easier version upgrade (e.g. change version in a yaml file instead of editing a script)
• In general, separate code and data

See https://github.com/RamenDR/ramen/pull/559#discussion_r1009347381

[nirs]

@ShyamsundarR I think we need new test label to make it easy to manage test enhancement issues.