Convert detectors to factory pattern, ability to set different model for each detector (#4635)

* refactor detectors

* move create_detector and DetectorTypeEnum

* fixed code formatting

* add detector model config models

* fix detector unit tests

* adjust SharedMemory size to largest detector model shape

* fix detector model config defaults

* enable auto-discovery of detectors

* simplify config

* simplify config changes further

* update detectors docs; detect detector configs dynamic

* add suggested changes

* remove custom detector doc

* fix grammar, adjust device defaults

frigate/detectors/__init__.py

@@ -0,0 +1,24 @@
+import logging
+
+from .detection_api import DetectionApi
+from .detector_config import (
+    PixelFormatEnum,
+    InputTensorEnum,
+    ModelConfig,
+)
+from .detector_types import DetectorTypeEnum, api_types, DetectorConfig
+
+
+logger = logging.getLogger(__name__)
+
+
+def create_detector(detector_config):
+    if detector_config.type == DetectorTypeEnum.cpu:
+        logger.warning(
+            "CPU detectors are not recommended and should only be used for testing or for trial purposes."
+        )
+
+    api = api_types.get(detector_config.type)
+    if not api:
+        raise ValueError(detector_config.type)
+    return api(detector_config)