Add UIHint for FlowJoin activity

The FlowJoin activity's join mode now includes a UIHint, which indicates its input is a dropdown. This improves user interface interaction by allowing the selection of join mode from a dropdown menu rather than manual input.

src/modules/Elsa.Workflows.Core/Activities/Flowchart/Activities/FlowJoin.cs

@@ -5,6 +5,7 @@
 using Elsa.Workflows.Activities.Flowchart.Models;
 using Elsa.Workflows.Attributes;
 using Elsa.Workflows.Models;
+using Elsa.Workflows.UIHints;
 using JetBrains.Annotations;
 
 namespace Elsa.Workflows.Activities.Flowchart.Activities;
@@ -26,7 +27,8 @@ public FlowJoin([CallerFilePath] string? source = default, [CallerLineNumber] in
  /// </summary>
  [Input(
  Description = "The join mode determines whether this activity should continue as soon as one inbound path comes in (Wait Any), or once all inbound paths have executed (Wait All).",
- DefaultValue = FlowJoinMode.WaitAny
+ DefaultValue = FlowJoinMode.WaitAny,
+ UIHint = InputUIHints.DropDown
  )]
  public Input<FlowJoinMode> Mode { get; set; } = new(FlowJoinMode.WaitAny);