Review fix

- Add `gcp-g4` gpuhunt flag
- Update `preview_features` description

Author: jvstme

src/dstack/_internal/core/backends/base/offers.py

@@ -23,6 +23,7 @@
     "oci-spot",
     "lambda-arm",
     "gcp-a4",
+    "gcp-g4",
     "gcp-dws-calendar-mode",
 ]
 

src/dstack/_internal/core/backends/gcp/models.py

@@ -92,7 +92,10 @@ class GCPBackendConfig(CoreModel):
     preview_features: Annotated[
         Optional[List[Literal["g4"]]],
         Field(
-            description=("The list of preview GCP features to enable. Supported values: `g4`"),
+            description=(
+                "The list of preview GCP features to enable."
+                " There are currently no preview features"
+            ),
             max_items=1,
         ),
     ] = None