make motion the default retain mode

docs/docs/configuration/index.md

@@ -273,7 +273,7 @@ record:
       #       here, the segments will already be gone by the time this mode is applied.
       #       For example, if the camera retain mode is "motion", the segments without motion are
       #       never stored, so setting the mode to "all" here won't bring them back.
-      mode: active_objects
+      mode: motion
       # Optional: Per object retention days
       objects:
         person: 15

frigate/config.py

@@ -72,9 +72,7 @@ class RetainModeEnum(str, Enum):
 
 class RetainConfig(FrigateBaseModel):
     default: float = Field(default=10, title="Default retention period.")
-    mode: RetainModeEnum = Field(
-        default=RetainModeEnum.active_objects, title="Retain mode."
-    )
+    mode: RetainModeEnum = Field(default=RetainModeEnum.motion, title="Retain mode.")
     objects: Dict[str, float] = Field(
         default_factory=dict, title="Object retention period."
     )