Remove mention of Bootz from the ManagementConfig message.

Fundamentally this is about skipping DHCP Boot not Bootz in particular. The SZTP RFC (And by extension the Bootz spec) specifies a "bootstrap-server-list" in the boot option. I chose bootstrap_server_uris because it is more descriptive as to what is actually supposed to go in the variable.

factory_reset/factory_reset.proto

@@ -45,7 +45,7 @@ message StartRequest {
 }
 
 message ManagementConfig {
-  repeated string bootz_uris = 1;
+  repeated string boot_server_uris = 1;
   string device_ip = 2;
   string mask_length = 3;
   string gateway_ip = 4;