Allow declaration types to specify field defaults

Problem/Motivation

Split off from ✨ Declaration types Active , including:

Send confirmation: (we should strongly warn that choosing yes is a good idea if 'oral'). This provides a default for a corresponding field on the declaration; the field is hidden by default but a site could choose to enable it for a bundle allow staff to have discretion over whether a declaration needs a confirmation).

Also other fields such as explanation??

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes