Add functionality to render individual components

[brancz]

kube-thanos has shaped up pretty nicely into a modular library. A concern that users still face is that they must render all components manually, even though they just pass a single config. See here for an example, not only is this leaky configuration with layering violations, it's inconvenient and error prone (it took multiple attempts to get certain parts right in the linked example.

It would be great if each individual component could offer .manifests field that could be recursively used to build the above without leaking configuration into the final rendering act.

@kakkoyun @metalmatze