Fixes: U4-4463 Upgrade 6.2.0 > 7.1.0 fails - due to incorrect formatting of foreign keys for sql servers

Conflicts:
	src/Umbraco.Tests/Migrations/AlterMigrationTests.cs
	src/Umbraco.Tests/Migrations/Stubs/AlterUserTableMigrationStub.cs
Merge remote-tracking branch 'origin/6.2.0' into 7.1.0

Conflicts:
	src/Umbraco.Tests/Migrations/Stubs/AlterUserTableMigrationStub.cs
Ensures correct exceptions are thrown when configurations cannot be loaded, before was just null ref exception which was not good.