When updating an enrollment, disallow provider type changes

[frankduncan]

When editing/renewing/resubmitting enrollments, it currently allows a change in provider type, which has certain drawbacks.

When thinking about how service admins use the system, there is a report specifically about enrollments by provider type over time. Allowing people to change it during the renew/edit/fix process could change how that report.

That may mean that in terms of people reviewing enrollments, provider type is central to their mindset when looking at an enrollment to review (maybe they even have different reviewers that specialize in different provider types), so effectively if someone were to change the provider type, it restarts the whole review process. We might as well make that explicit, and then it simplifies the branching logic changes substantially.

[frankduncan]

This is related to #949, and the enrollment provider lifecycle project as a whole

[PaulMorris]

See also #833 .

[PaulMorris]

For development purposes, when working with the application steps UI which can differ for different provider types, I've found it helpful to create a draft application that has been filled out completely (just not submitted). Then I can edit that draft and change its provider type, allowing me to access the UI for other types, without having to redo all of the data entry that they have in common.

(For this to work you need a draft individual provider type and a draft organization provider type, and use the corresponding one for looking at other individual or other organization provider types.)

That may or may not be a consideration. Maybe allow changing the provider type on not-yet-submitted drafts, but disallow it when editing submitted applications, renewals, etc.