[Language] Rename DocumentType to HealthcareDocumentType (Azure#21382)

Author: mssfang

specification/cognitiveservices/data-plane/Language/preview/2022-10-01-preview/analyzetext.json

@@ -785,7 +785,7 @@
         },
         "documentType": {
           "x-ms-enum": {
-            "name": "documentType",
+            "name": "healthcareDocumentType",
             "modelAsString": true
           },
           "type": "string",