Added back CMD command

[hleroy]

Commit 634b091 introduced an issue. Clearning the ENTRYPOINT also clears the CMD. We need to set explicitly CMD again.

Description

Set CMD in derived Dockerfile (use same CMD as original Amazon aws-cli container).

Checklist:

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

Rationale

Fix cookiecutter#5241

[browniebroke]

Did you mean to open this against https://github.com/cookiecutter/cookiecutter-django? The base branch is on your fork 😄

[luzfcb]

closed in cookiecutter#5245