Tag model manager v2 api as unstable (#5311)

## What type of PR is this? (check all applicable)

- [X] Refactor
- [ ] Feature
- [ ] Bug Fix
- [ ] Optimization
- [ ] Documentation Update
- [ ] Community Node Submission


## Have you discussed this change with the InvokeAI team?
- [X] Yes
- [ ] No, because:

      
## Have you updated all relevant documentation?
- [X] Yes
- [ ] No


## Description

As discussed with @psychedelicious , this PR changes the swagger label
on the model manager V2 routes to `model_manager_v2_unstable` in order
to warn community members that the API is liable to change.

## Related Tickets & Documents

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## Added/updated tests?

- [ ] Yes
- [ ] No : _please replace this line with details on why tests
      have not been included_

## [optional] Are there any post deployment tasks we need to perform?

invokeai/app/api/routers/model_records.py

@@ -26,7 +26,7 @@ from invokeai.backend.model_manager.config import (
 
 from ..dependencies import ApiDependencies
 
-model_records_router = APIRouter(prefix="/v1/model/record", tags=["model_manager_v2"])
+model_records_router = APIRouter(prefix="/v1/model/record", tags=["model_manager_v2_unstable"])
 
 
 class ModelsList(BaseModel):