ConfigMap-style volumes and matching container mounts

Define a new type of volume configuration, similar to the Kubernetes ConfigMap. It may support nesting the config files in subdirectories. The running idea is:

apiVersion: v1alpha1
kind: ConfigVolumeConfig
name: my-foobar-configs
files:
  foo.conf: |
    [section-abc]
    key1=val1
    key2=val2
  bar.yaml: |
    key1: val1
    key2: val2
  subdir/baz.ini: |
    key1=val1

Talos Containers will leverage that to mount a static, read-only FS tree into a container. The mount path will be defined via the ContainerConfig, as follows:

apiVersion: v1alpha1
kind: ContainerConfig
name: foobar
image: foobar:1.2.3
mounts:
  - configVolume:
      name: my-custom-configs
      destination: /etc/foobar/something

From the container's mount ns, the effective mount will appear as:

/etc/foobar/something
  | foo.conf
  | bar.yaml
   -- subdir
       | baz.ini

Resource naming may change. I think ConfigVolumeConfig may be a bit confusing and detrimental to UX - perhaps TextFilesConfig?