fix embargoed dandiset creation form

[bendichter]

Currently, the embargoed dandiset creation formform looks like this:

This has some problems:

• It requires the award to be NIH (via regex)
• It does not provide a place for users to indicate with the grant ends
• It does not allow for projects that don't correspond to research grants.

Proposed solution (discussed with @satra):

• Toggle for have award vs. don't have award. Have award should be default.
• If award:
  • Form fields:
    • Funding source (required)
    • Grant number (not required, no regex)
    • Grant end date (required)
  • If Funding source and Grant number, funding source is added as a Contributor to the Dandiset.
• If not award, automatically show the embargo end date, which is 2 years from the current date.