s/priority/rank in TaskTemplate (#2184)

Purely internal, proto name change. Working through some backend
refactors and this naming avoids a conflict with another notion of
inter-function priorities in the scheduler. Also align naming with new
{target,max}-concurrent-inputs spec (on a per task-template basis).

modal/functions.py

@@ -832,7 +832,7 @@ async def _load(self: _Function, resolver: Resolver, existing_object_id: Optiona
                     _experimental_concurrent_cancellations=True,
                     _experimental_task_templates=[
                         api_pb2.TaskTemplate(
-                            priority=1,
+                            rank=1,
                             resources=convert_fn_config_to_resources_config(
                                 cpu=cpu, memory=memory, gpu=_experimental_gpu, ephemeral_disk=ephemeral_disk
                             ),

modal_proto/api.proto

@@ -2081,9 +2081,10 @@ message TaskStats {
 }
 
 message TaskTemplate {
-  uint32 priority = 1;
+  uint32 rank = 1;
   Resources resources = 2;
-  uint32 concurrent_inputs = 3;
+  uint32 target_concurrent_inputs = 3;
+  uint32 max_concurrent_inputs = 4;
 }
 
 message TokenFlowCreateRequest {