Run Function as non-root user

[ccfontes]

Error when runnng as non-root user:

Function invoke time error:
   mkdir: cannot create directory '/home/app/.pack/.tmp0': Permission denied
   /home/app/.pack/bin/idris2: 7: [: missing ]
 FIXME: fix errors above for this user:

Dockerfile related code:

 RUN groupadd app && useradd -g app app
 USER app:app