feat: PoC for dynamic constraints using standard cds views

bookshop/srv/x-field-control.cds

@@ -0,0 +1,10 @@
+namespace sap.capire.bookshop;
+using from '../db/schema';
+
+view Books.field.control as select from Books { ID,
+  genre.name == 'Drama' ? 'readonly' :
+  null as price
+}
+extend Books with {
+  fc : Association to Books.field.control on fc.ID = $self.ID
+}