Phase creation from ui with starting_kit/public_data bug fixed

[ihsaan-ullah]

Description

Creating a compeittion from UI where phase has public data or starting kit was failing because from the front end the startingkit/pub_data was sent as a dict instead of their ids. Now with this change, the dict is converted to ids just like it is done in the competition update method.

Issues this PR resolves

• Problem creating Phase: Errors(s) saving benchmark: phases: public_data: Incorrect type. Expected pk value, received dict. #1801

A checklist for hand testing

• Create a new competition using the UI, Add public data and starting kit to a new phase, check that you don't get any error.
• When competition is created, check that the public data and starting kit are properly added to the competition.

Checklist

• Code review by me
• Hand tested by me
• I'm proud of my work
• Code review by reviewer
• Hand tested by reviewer
• CircleCi tests are passing
• Ready to merge