Package snap components

[mr-cal]

What needs to get done

Each component’s prime directory and its metadata file should be packaged with snap pack.

The packaged components should be placed alongside the snap package.

The final message of snapcraft should include the packaged components. For example:

Snapped hello_world_1.0_amd64.snap and components `hello-world+foo_1.0.comp`, `hello-world+bar_1.0.comp`, and `hello-world+baz_1.0.comp`.

Why it needs to get done

To support components in snapcraft

[mr-cal]

Completed via #4506