Change engine/.env to be committed and have .env.local override (#6150)

# Description of Changes
We keep adding stuff to `engine/config/.env.example` and have to
manually update `.env` because of it, which is really clunky, especially
when working on multiple worktrees at once. This PR changes it so that
we just have a committed `.env` file and have an `.env.local` override
to put the actual private keys into, which should make it a bit easier
to manage.

> [!warning]
>
> After this goes in, be very careful for a little while not to
accidentally commit any keys that you've got inside your `.env` file!

engine/Dockerfile

@@ -12,9 +12,8 @@ RUN apt-get update \
 
 WORKDIR /app
 
-COPY pyproject.toml uv.lock Taskfile.yml ./
+COPY pyproject.toml uv.lock Taskfile.yml .env ./
 COPY .taskfiles/ ./.taskfiles/
-COPY config/ ./config/
 COPY scripts/ ./scripts/
 RUN --mount=type=cache,target=/root/.cache/uv \
     uv sync --frozen --no-dev