Adding change to support OcrSkillLanguage value of "unk" (Azure#16279)

* Adding change to support OcrSkillLanguage value of "unk"

* Adding clarification about OcrSkillLanguage unk value.

Author: gmndrg

specification/search/data-plane/Azure.Search/preview/2020-06-30-Preview/searchservice.json

@@ -8574,7 +8574,8 @@
         "ro",
         "sr-Cyrl",
         "sr-Latn",
-        "sk"
+        "sk",
+        "unk"
       ],
       "x-ms-enum": {
         "name": "OcrSkillLanguage",
@@ -8683,6 +8684,10 @@
           {
             "value": "sk",
             "description": "Slovak"
+          },
+          {
+            "value": "unk",
+            "description": "Unknown.  If the language is explicitly set to \"unk\", the language will be auto-detected."
           }
         ]
       },