feat: add compatibilityVersioning for distro-aware Docker tag updates

[thejoeejoee]

Problem

Compound Docker tags like python:3.12-bookworm combine a semantic version with a distro compatibility identifier. Currently, Renovate can only update the version part, not the distro suffix. This limits use cases where both the Python version AND the Debian/Ubuntu distro version should be kept in sync.

Related discussions:

• How to use two versioning schemes for the same dependency in the same file #22836: "How to use two versioning schemes for the same dependency"
• dockerfile manager: allow debian and ubuntu versioning for parts of tags #38371: "Allow debian and ubuntu versioning for parts of tags"

Proposed Solution

Introduce a compatibilityVersioning configuration option that applies distro-aware versioning (debian/ubuntu) to the compatibility part of the tag instead of requiring exact matching.

Configuration Example

{
  "packageRules": [{
    "matchDatasources": ["docker"],
    "matchPackageNames": ["python"],
    "versionCompatibility": "^(?<version>[^-]+)-(?<compatibility>.+)$",
    "compatibilityVersioning": "debian",
    "versioning": "semver"
  }]
}

Expected Behavior

• python:3.12-bookworm → python:3.14-trixie (updates both version and distro)
• With compatibilityVersioning: "debian", the compatibility part follows Debian versioning rules

Implementation Notes

The versionCompatibility regex already splits tags into version and compatibility capture groups. The compatibilityVersioning option would:

1. Apply a distro versioning module (debian/ubuntu/etc.) to the compatibility part
2. Use that module to filter available versions instead of exact matching
3. Reconstruct the new value using both updated parts

Phased Approach

• Phase 1: Combined updates (single tag with both parts updated)
• Phase 2: Separate distro PRs (option to create independent PRs for version vs. distro updates)
• Phase 3: Alpine Linux support with alternative versioning schemes

Technical Details

The critical implementation detail is fixing newValue reconstruction. Currently it uses String.replace() which does not handle compatibility-only changes correctly. A proper split/join pattern with the regex groups is needed.

This feature enables better Docker versioning strategies for production deployments using pinned distro-specific tags.