Add unit test to check for pending schema changes

[chenriksson]

Suggested by @joelverhagen to keep migrations and schema changes in sync

Should be possible to programmatically create migration and check. See:

• https://github.com/aspnet/EntityFrameworkCore/blob/dev/test/ef.Tests/SimpleProjectTest.cs
• https://github.com/aspnet/EntityFrameworkCore/blob/dev/src/ef/Commands/MigrationsAddCommand.cs

[skofman1]

@chenriksson , which DB do we want to test this on?

[chenriksson]

@skofman1 This isn't testing migrations against a DB instance. The test would check if EF would detect schema changes if a new migration were added... comparing the source code against the latest EF migration snapshot.

Will keep, but put at P3

[joelverhagen]

Done on gallery DB, support requests DB, and validation DB.