`talosctl gen config` to output a single config type

[smira]

Add a flag to output a single config type (controlplane/worker/talosconfig) instead of a bundle, specify destination file (we can default to stdout).

[smira]

Please note that gen config already supports creating reproducible base config from a secrets bundle, and add patches on top of it, so this issue is only about changing the output format.

[andrewrynhard]

User wants something like:

talosctl gen config --from=base.yaml --config-patch=patch.yaml

from is an existing base machine configuration.

[smira]

I don't like gen config with --from, how about talosctl machineconfig patch -f base.yaml -p @patch1.yaml ?