Allow to search in soft-deleted items

A new query/request parameter can be used to apply a search to only
soft-deleted items.

The query expression `Trashed` has been introduced which selects only
items with state `Deleted`. This is another option an analog to
`ValidItemStates` (both cannot be used together as they would select
no items). This new query node is not added to the parser, because
users may not use it in their own queries - it must be part of the
"fixed" query so the application can control in which subset to search
(it would otherwise be possible to select any items).

modules/query/shared/src/main/scala/docspell/query/ItemQuery.scala

@@ -125,7 +125,8 @@ object ItemQuery {
     final case class ChecksumMatch(checksum: String) extends Expr
     final case class AttachId(id: String)            extends Expr
 
-    case object ValidItemStates extends Expr
+    final case object ValidItemStates extends Expr
+    final case object Trashed         extends Expr
 
     // things that can be expressed with terms above
     sealed trait MacroExpr extends Expr {

modules/query/shared/src/main/scala/docspell/query/internal/ExprUtil.scala

@@ -75,9 +75,10 @@ object ExprUtil {
         expr
       case AttachId(_) =>
         expr
-
       case ValidItemStates =>
         expr
+      case Trashed =>
+        expr
     }
 
   private def spliceAnd(nodes: Nel[Expr]): Nel[Expr] =