feat: Add devcontainer

[faucomte97]

Adds a devcontainer for the portal repo. In theory, this means it can be built and run in VS Code either from this repo/folder directly or from the workspace folder.

Steps to run:

1. Install the dev containers extension in VS Code.
2. Open devcontainer.json.
3. Run the Dev Containers: Rebuild and Reopen in Container command. The dev container will then proceed to building. This might take a while the first time you run this depending on your internet speed and / or any VPNs or DDoS mitigation software (the latter might prevent the container from being built entirely).
4. Once the dev container is built and running, you need to specify the Python interpreter using the Python: Select Interpreter command (not sure if this can be automated / is needed).
5. Then, you should just be able to run the project locally using the Run & Debug tab.

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This change is 

[faucomte97]

No longer relevant