Advertise sliding-sync support when using conduit

Starting from version `0.6.0` conduit natively supports some sync v3 (sliding-sync) features.

https://gitlab.com/famedly/conduit/-/releases/v0.6.0
https://gitlab.com/famedly/conduit/-/merge_requests/501

roles/custom/matrix-base/templates/static-files/well-known/matrix-client.j2

@@ -30,6 +30,10 @@
 	"org.matrix.msc3575.proxy": {
 		"url": "{{ matrix_sliding_sync_base_url }}"
 	}
+ 	{% elif matrix_homeserver_implementation == 'conduit' %},
+	"org.matrix.msc3575.proxy": {
+		"url": "{{ matrix_homeserver_url }}"
+	}
 	{% endif %}
 	{% if matrix_client_element_location_sharing_enabled %},
 	"m.tile_server": {