release/8.10 Move modules-update to custom build and gate redis_repo

[dariaguy]

Note

Medium Risk
Changes affect how release images fetch module sources and enforce release source repo policy; misconfiguration could break custom module builds or block legitimate release dispatches.

Overview
Release workflow now rejects run_type=release when redis_repo is not redis/redis, so official release builds cannot pull Redis from a fork (forks remain allowed for custom/unstable/nightly runs).

Standard release Docker images (committed alpine/debian Dockerfiles) no longer run the bundled modules-update / .prepared skip logic during module builds—they go straight to Rust install and make deploy.

Custom builds (via Dockerfile.j2 with custom_build) still pin module refs with yq, optionally skip modules-update when bundled .prepared sources exist and no module version overrides were passed, and otherwise run modules-update; that whole block is now wrapped entirely inside the custom_build template branch.

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