Refactor findItemsWithTags to more general useful

modules/fts-client/src/main/scala/docspell/ftsclient/FtsClient.scala

@@ -24,6 +24,7 @@ trait FtsClient[F[_]] {
   /** Run a full-text search. */
   def search(q: FtsQuery): F[FtsResult]
 
+  /** Continually run a full-text search and concatenate the results. */
   def searchAll(q: FtsQuery): Stream[F, FtsResult] =
     Stream.eval(search(q)).flatMap { result =>
       if (result.results.size < q.limit) Stream.emit(result)

modules/fts-client/src/main/scala/docspell/ftsclient/FtsQuery.scala

@@ -8,7 +8,8 @@ import docspell.common._
   * interpret it according to the system in use.
   *
   * Searches must only look for given collective and in the given list
-  * of item ids.
+  * of item ids, if it is non-empty. If the item set is empty, then
+  * don't restrict the result in this way.
   */
 final case class FtsQuery(
     q: String,