feat(app): generic progress events

Some processes have steps, like denoising or a tiled spandel.

Denoising has its own step callback but we don't have any generic way to signal progress. Processes like a tiled spandrel run show indeterminate progress in the client.

This change introduces a new event to handle this: `InvocationGenericProgressEvent`

A simplified helper is added to the invocation API so nodes can easily emit progress as they do their thing.

invokeai/app/api/sockets.py

@@ -22,6 +22,7 @@ from invokeai.app.services.events.events_common import (
     InvocationCompleteEvent,
     InvocationDenoiseProgressEvent,
     InvocationErrorEvent,
+    InvocationGenericProgressEvent,
     InvocationStartedEvent,
     ModelEventBase,
     ModelInstallCancelledEvent,
@@ -56,6 +57,7 @@ class BulkDownloadSubscriptionEvent(BaseModel):
 QUEUE_EVENTS = {
     InvocationStartedEvent,
     InvocationDenoiseProgressEvent,
+    InvocationGenericProgressEvent,
     InvocationCompleteEvent,
     InvocationErrorEvent,
     QueueItemStatusChangedEvent,