Fix RDBMS filter construction for applications and flags

* Add a new byFlag resource filter feature to support filtering
  using flags.
  False by default since only system applications use it.
* Add filter definitions to flag pkg resource.
* Add support for using []string inside byValue filters.

codegen/schema/resource.cue

@@ -42,6 +42,9 @@ import (
 		// filtering by label
 		labels:   bool | *true
 
+		// filtering by flag
+		flags:   bool | *false
+
 		// support pagination
 		paging:   bool | *true