Problem

The CI test infrastructure maintains 3 nearly-identical copies of each containerfile and blueprint for EC, RC, and zstream releases. This causes:

• Wasted build time building all 3 images when only one is needed
• Poor S3 cache utilization with separate entries per release type
• Maintenance overhead updating 3+ files for any change
• Inconsistent naming conventions between bootc and OSTree images

Solution

Replace the 3 variants with a single unified `lrel` (latest release) template that automatically selects the appropriate version using priority logic:

zstream > RC > EC

Scope

• Consolidate bootc containerfiles (group1 + group2)
• Consolidate OSTree toml blueprints (group3 + group4)
• Update `common_versions.sh` with priority selection logic
• Update all scenario files to use fixed `lrel` naming
• Standardize image naming: rhel96-{type}brew-lrel{variant}