chore: update rockcraft project, add sanity test, and tox.ini file

[NohaIhab]

closes #84

Summary

• Updates the rockcraft.yaml to 1.8 version for CKF 1.8
• Refactors the rockcraft.yaml to be consistent with the Dockerfile's copying files and building
• Modifies the pebble service name to match the 1.8 charm
• Adds tox file to run the workflows on the volumes rockcraft project
• Adds sanity tests to check the expected files exist in the rock
• Adds .gitignore to the repo to avoid committing unwanted files

Testing

1. Build the rock

   tox -e pack

2. Export the rock to Docker

   tox -e export-to-docker

3. Run a container with the image and replace the entrypoint with a shell

   docker run --rm -ti volumes-web-app:1.8.0 exec /bin/bash

4. Go to the working-dir /src

   cd /src

5. Run the entrypoint command

   _daemon_@f2a80c2d3f9f:/src$ gunicorn -w 3 --bind 0.0.0.0:5000 --access-logfile - entrypoint:app

   Expected output:

   [2024-05-20 12:20:09 +0000] [22] [INFO] Starting gunicorn 22.0.0
   [2024-05-20 12:20:09 +0000] [22] [INFO] Listening at: http://0.0.0.0:5000 (22)
   [2024-05-20 12:20:09 +0000] [22] [INFO] Using worker: sync
   [2024-05-20 12:20:09 +0000] [23] [INFO] Booting worker with pid: 23
   [2024-05-20 12:20:09 +0000] [24] [INFO] Booting worker with pid: 24
   [2024-05-20 12:20:09 +0000] [25] [INFO] Booting worker with pid: 25
   [2024-05-20 12:20:12 +0000] [23] [ERROR] Exception in worker process
   ...

   Because the container image needs kubeconfig and proper expose of a the serving port, the expected output will be followed by the following errors:

   kubernetes.config.config_exception.ConfigException: Service host/port is not set.
   kubernetes.config.config_exception.ConfigException: Invalid kube-config file. No configuration found.

   Another test you can do is run the upstream image and compare the output, it should be the same:

   docker run docker.io/kubeflownotebookswg/volumes-web-app:v1.8.0