Check primary keys for all tables and drop ForeignReference (#21721)

Some dbs require that all tables have primary keys, see
- #16802
- #21086

We can add a test to keep it from being broken again.

Edit:

~Added missing primary key for `ForeignReference`~ Dropped the
`ForeignReference` table to satisfy the check, so it closes #21086.

More context can be found in comments.

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: zeripath <art27@cantab.net>

models/migrations/migrations.go

@@ -444,6 +444,8 @@ var migrations = []Migration{
 	NewMigration("Add index for access_token", v1_19.AddIndexForAccessToken),
 	// v236 -> v237
 	NewMigration("Create secrets table", v1_19.CreateSecretsTable),
+	// v237 -> v238
+	NewMigration("Drop ForeignReference table", v1_19.DropForeignReferenceTable),
 }
 
 // GetCurrentDBVersion returns the current db version