Fixing docker internal hosts (option 2)

[amazingphilippe]

Summary | Résumé

This will need a proper review. While it works, I'm not sure why.

Essentially, this PR should use docker-compose.yml to make sure we use a new "notification-network" in both api and admin ymls. See related PR here: cds-snc/notification-api#2340

Did I configure Dockerfile, devcontainer.json properly? I doubt it.

Additionally, when opening this container, Poetry complained about not being able to install "notification-admin". Possibly because packages is empty in pyproject.toml? Again, please code check me!

Test instructions | Instructions pour tester la modification

Sequential steps (1., 2., 3., ...) that describe how to test this change. This
will help a developer test things out without too much detective work. Also,
include any environmental setup steps that aren't in the normal README steps
and/or any time-based elements that this requires.

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Étapes consécutives (1., 2., 3., …) qui décrivent la façon de tester la
modification. Elles aideront les développeurs à faire des tests sans avoir à
jouer au détective. Veuillez aussi inclure toutes les étapes de configuration
de l’environnement qui ne font pas partie des étapes normales dans le fichier
README et tout élément temporel requis.

[github-actions]

🧪 Review environment

https://4pedgxk25wwkn6emfpdkqe57zm0mhytd.lambda-url.ca-central-1.on.aws/

[amazingphilippe]

Closing this for #1986