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

This commit adds a new `show_filters_icon` 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 `_show_filters_icon` attribute to Link class (default: True)
- Added `show_filters_icon` property getter
- Added `update_show_filters_icon()` method for updating the property
- Updated `asdict()` to include the new field in both topology and regular dumps
- Added `show_filters_icon` field to LinkBase schema
- Updated API routes to handle the new field in create and update operations

**API Impact:**
- POST /v3/projects/{project_id}/links - accepts `show_filters_icon` in request body
- PUT /v3/projects/{project_id}/links/{link_id} - can update `show_filters_icon`
- GET /v3/projects/{project_id}/links/{link_id} - returns `show_filters_icon` 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/schemas/controller/links.py

@@ -62,6 +62,7 @@ class LinkBase(BaseModel):
     suspend: Optional[bool] = None
     link_style: Optional[LinkStyle] = None
     filters: Optional[dict] = None
+    show_filters_icon: Optional[bool] = None
 
 
 class LinkCreate(LinkBase):