feat: add rock goss checks on PRs

[lucabello]

Issue

Rocks currently have no tests on PR, making it impossible to know if they're working (besides trying to pack them), which in turn prevents us from auto-merging them.

Solution

Use noctua and goss to:

1. run a packed rock in a Kubernetes pod
2. install goss in the pod, and copy the goss.yaml file into it
3. run goss validate inside it

Testing Instructions

Get noctua (here, you can pip install it from git) and this rock repo (or any rock repo, if you write the goss.yaml).

1. cd <version> && rockcraft pack
2. noctua rock test <rock_file> --goss-file=../goss.yaml --one-shot
3. Watch the magic happen