feat: add compose exec and compose bash commands

Exec is new command scoped under compose. It allows sending commands
directly into appserver container. I will make this
customizable/controllable in the future.

src/cli/django.rs

@@ -31,7 +31,7 @@ pub enum Django {
 
     /// Run Django's manage.py shell.
     Shell,
-    
+
     /// Run Django's manage.py test.
     Test,
 }