Adding enum encoding AGIPD gain mode

cal_tools/cal_tools/enums.py

-from enum import Enum, IntFlag
+from enum import Enum, IntEnum, IntFlag
 
 
 class BadPixels(IntFlag):
@@ -48,3 +48,12 @@ class SnowResolution(Enum):
     """
     NONE = "none"
     INTERPOLATE = "interpolate"
+
+
+class AgipdGainMode(IntEnum):
+    """Encoding added to distinguish between adaptive and fixed gain"""
+
+    ADAPTIVE_GAIN = 0  # adaptive is default (if gain mode missing in slow data)
+    FIXED_HIGH_GAIN = 1  # non-zero means fixed gain
+    FIXED_MEDIUM_GAIN = 2
+    FIXED_LOW_GAIN = 3