Add explicit type annotations to nullable columns

TypeORM can't correctly infer the data type on properties with a `| null` type.
This commit adds explicit type annotations.

See also https://github.com/typeorm/typeorm/issues/2567#issuecomment-408599335

Signed-off-by: David Mehren <git@herrmehren.de>

src/users/user.entity.ts

@@ -40,11 +40,13 @@ export class User {
 
   @Column({
     nullable: true,
+    type: 'text',
   })
   photo: string | null;
 
   @Column({
     nullable: true,
+    type: 'text',
   })
   email: string | null;