R1:53d5cd395077

Allow EditEngine forms to have defaults assigned

Summary: Ref T9132. Allow form configurations to include defaults (like default projects, spaces, policies, etc).

Test Plan:
Defaulted "Language" to "Rainbow", plus other adjustments:

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Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9132

Differential Revision: https://secure.phabricator.com/D14508