Support custom (Docker) bind mounts for Talos-in-Docker clusters

[PhilipSchmid]

Feature Request

Allow specifying custom (Docker) volume (bind) mounts when starting a Talos-in-Docker cluster using talosctl cluster create.

Description / Background

Knowing which kernel modules are present in the underlying host's kernel is essential for some (primarily infra-related) workloads like Cilium.

For example, having direct access via a bind mount to the host's /lib/modules is required for proper kernel module validation. Because of that, we're "bind" mounting /lib/modules:/lib/modules in Cilium's KIND-based testing setup. This also applies to the provided devcontainer setup and even for the Cilium agent DaemonSet from the official Helm chart.

Difficulty: The actually used kernel version (uname -r) doesn't match what's available within /lib/modules/:

root@talos-default-controlplane-1:/home/cilium# uname -r
6.10.4-linuxkit
root@talos-default-controlplane-1:/home/cilium# ls -l /lib/modules/
total 4
drwxr-xr-x 3 root root 4096 Sep 23 13:23 6.6.52-talos

No, unfortunately, Running Talos in Docker Manually with a manually added --mount source=/lib/modules,target=/lib/modules,type=bind,readonly isn't really a feasible alternative, as some talosctl parameters set up specific Talos internal things (--config-patch-control-plane, --cidr, --kubernetes-version, etc.) which can't be done via simple docker run ... ghcr.io/siderolabs/talos.