Sync authHeaders in RestService From DataFactory To Synapse (Azure#21475)

* Sync authHeaders in RestService From DataFactory To Synapse

* update

Author: Jingshu923

specification/synapse/data-plane/Microsoft.Synapse/preview/2021-06-01-preview/entityTypes/LinkedService.json

@@ -2745,6 +2745,10 @@
           "description": "The password used in Basic authentication type.",
           "$ref": "../artifacts.json#/definitions/SecretBase"
         },
+        "authHeaders": {
+          "type": "object",
+          "description": "The additional HTTP headers in the request to RESTful API used for authorization. Type: object (or Expression with resultType object)."
+        },
         "servicePrincipalId": {
           "description": "The application's client ID used in AadServicePrincipal authentication type.",
           "type": "object"

specification/synapse/data-plane/Microsoft.Synapse/stable/2020-12-01/entityTypes/LinkedService.json

@@ -2843,6 +2843,10 @@
           "description": "The password used in Basic authentication type.",
           "$ref": "../artifacts.json#/definitions/SecretBase"
         },
+        "authHeaders": {
+          "type": "object",
+          "description": "The additional HTTP headers in the request to RESTful API used for authorization. Type: object (or Expression with resultType object)."
+        },
         "servicePrincipalId": {
           "description": "The application's client ID used in AadServicePrincipal authentication type.",
           "type": "object"