Update Dockerfile

[jtac]

creating the workspace directory after switching user to fix permission errors https://github.com/OpenDevin/OpenDevin/issues/1560

[iFurySt]

@jtac the workflow failed, can you take a look?

> Dockerfile:56
> --------------------
>   54 |     RUN chown -R opendevin:app /app && chmod -R 770 /app
>   55 |     USER opendevin
>   56 | >>> RUN mkdir -p $WORKSPACE_BASE
>   57 |     
>   58 |     ENV VIRTUAL_ENV=/app/.venv \
> --------------------
> ERROR: failed to solve: process "/bin/sh -c mkdir -p $WORKSPACE_BASE" did not complete successfully: exit code: 1
> Error: Process completed with exit code 1.

[rbren]

User probably doesn't have permission to edit the /opt dir. Maybe we should create it as root, then chown it?

[jtac]

I moved the creation back to root and instead added a line to assign the directory to the user