feat: add show_filters_icon property to Link for controlling Web UI filter icon display

This commit adds a new  property to the Link class, allowing users to control whether filter icons are displayed in the Web UI at the individual link level.

**Changes:**
- Added  attribute to Link class (default: True)
- Added  property getter
- Added  method for updating the property
- Updated  to include the new field with backward compatibility
- Added  field to LinkBase schema using Optional[bool] = Field(True, ...) pattern
- Updated API routes to handle the new field in create and update operations
- Added loading logic for show_filters_icon in project.open() to preserve settings when reopening projects

**Schema Definition:**
Uses the same pattern as the  field:

**API Impact:**
- POST /v3/projects/{project_id}/links - accepts  in request body
- PUT /v3/projects/{project_id}/links/{link_id} - can update
- GET /v3/projects/{project_id}/links/{link_id} - returns  field

**Future Applications:**
This feature provides granular control for future AI fault injection modules to manage link-level protocol failures while maintaining clean UI presentation.

gns3server/controller/project.py

@@ -1208,6 +1208,8 @@ class Project:
                     await link.update_filters(link_data["filters"])
                 if "link_style" in link_data:
                     await link.update_link_style(link_data["link_style"])
+                if "show_filters_icon" in link_data:
+                    await link.update_show_filters_icon(link_data["show_filters_icon"])
                 for node_link in link_data.get("nodes", []):
                     node = self.get_node(node_link["node_id"])
                     port = node.get_port(node_link["adapter_number"], node_link["port_number"])