Fix overrideCommand value in devcontainer so that the django container can run (#4517)

[Tharushan]

Description

A simple bugfix on devcontainer that prevented the django container from running when using VSCode with use_docker=y

How to reproduce the bug:

• Just generate a new project using : cookiecutter gh:cookiecutter/cookiecutter-django with use_docker=y
• Open the generated project with VSCode then you will see this popup: "Do you want to install the recommended 'Dev Containers' extension from Microsoft for this repository?" then to open it :
  
• After the devcontainer is built and started you will see that services are up but can't access them with http://localhost:8000 or https://localhost:8000

DevContainer documentation on this : https://containers.dev/implementors/json_reference/

Which states that this property should be set to

false when referencing a Docker Compose file

which is set here :

    "dockerComposeFile": [
        "../local.yml"
    ],

Checklist:

• I've made sure that tests are updated accordingly (especially if adding or updating a template option)
• I've updated the documentation or confirm that my change doesn't require any updates

Rationale

No open issue pointing this bug, asked on the Discord Channel if this property was set to true for a particular reason