Issue #3590179: Add Renovate to auto update dependencies

• Adds Renovate for automated dependency updates, for major versions in composer and only for astro packages (to start with, as a test) on npm
• Configures a GitLab CI job that runs Renovate on a scheduled pipeline
• minor and patch updates are grouped into a single MR to reduce noise - major updates remain separate

Closes #3590179 (closed)