### Check existing issues - [x] I've verified that this request isn't described by any existing issues. ### Request It's already possible to use `stage-snaps` in a snapcraft.yaml to compose multiple snaps into a bigger one, or to dump the contents of a list of snaps into a ROCK (in the case of rockcraft.yaml). It would be great if there was a similar way to stage snap components, either extending the syntax of `stage-snaps` to support constructs like `snap+component` or a more specific key `stage-snap-components` in which the items in the list follow the syntax (`snap+component`) (or a better UX you might find that I can't think of right now). ### The problem it solves Allowing this composition aligns the reuse of snaps and snaps components in a finer grained way when composing larger units of deployments, such as composite snaps or ROCKs. I believe such feature should allow decoupling the component from the main snap. Although that could be somewhat surprising for folks used to `snap download snap+component` to acquire both, for `snapcraft.yaml` and other craft-related configurations, certain use cases might benefit from solely bringing the component, such as locale data that happens to be replicated in multiple snaps without having to source one of the main snaps in that case. An optional component in a snap might be a useful dependency of a composite snap.