Restrict proposals for due date

Avoid dates too far in the future.

modules/common/src/main/scala/docspell/common/Duration.scala

@@ -53,6 +53,9 @@ object Duration {
   def days(n: Long): Duration =
     apply(JDur.ofDays(n))
 
+  def years(n: Long): Duration =
+    days(n * 365)
+
   def nanos(n: Long): Duration =
     Duration(n)