Add export_filename option to modeladmin

docs/reference/contrib/modeladmin/indexview.rst

@@ -293,6 +293,21 @@ for your model. For example:
         list_filter = ('is_staff', 'company')
 
 
+.. _modeladmin_export_filename:
+
+------------------------------
+``ModelAdmin.export_filename``
+------------------------------
+
+**Expected value**: A string specifying the filename of an exported spreadsheet,
+without file extensions.
+
+.. code-block:: python
+
+    class PersonAdmin(ModelAdmin):
+        export_filename = 'people_spreadsheet'
+
+
 .. _modeladmin_search_fields:
 
 ----------------------------

wagtail/contrib/modeladmin/views.py

@@ -265,6 +265,10 @@ class IndexView(SpreadsheetExportMixin, WMABaseView):
 
         return super().dispatch(request, *args, **kwargs)
 
+    def get_filename(self):
+        """ Get filename for exported spreadsheet, without extension """
+        return getattr(self.model_admin, 'export_filename', super().get_filename())
+
     def get_heading(self, queryset, field):
         """ Get headings for exported spreadsheet column for the relevant field """
         heading_override = self.export_headings.get(field)