Add an option to skip migrations when the application is starting.

[decko]

Closes #544

[mdellweg]

What is the plan with this? I see adding another layer of complexity on top of what is already much too complex.
The issue description was: Stop running setup code in the api container.

So the question here is: How are the pulp-minimal containers to be used?
I see:

• compose files in this repository (we control them).
• pulp_operator (we can tell it to run a setup routine).

[decko]

After some discussion we decided to go on with another idea. Closing it for now.