Fix response-validation 500s on sensor encoding types

Author: daniel-slaugh

interfaces/sensorthings/schemas/sensor.py

@@ -20,13 +20,19 @@ class SensorModel(Schema):
     )
 
 
-sensorEncodingTypes = Literal[
+KnownSensorEncodingTypes = Literal[
     "application/pdf",
     "http://www.opengis.net/doc/IS/SensorML/2.0",
     "text/html",
     "application/json",
+    "text/plain",
 ]
 
+# Legacy deployments may contain other valid MIME strings in this field.
+# Keep known values documented while accepting arbitrary encodings to avoid
+# response-validation 500s when reading existing records.
+sensorEncodingTypes = KnownSensorEncodingTypes | str
+
 
 class SensorMetadata(Schema):
     method_code: Optional[str] = None