message: add pbi workspace linked service
diff: "required": [
  "endpoint"
  ]
  + },
  + "PowerBIWorkspaceLinkedService": {
  + "x-ms-discriminator-value": "PowerBIWorkspace",
  + "description": "Power BI Workspace linked service.",
  + "type": "object",
  + "allOf": [
  + {
  + "$ref": "#/definitions/LinkedService"
  + }
  + ],
  + "properties": {
  + "typeProperties": {
  + "description": "Power BI Workspace linked service properties.",
  + "x-ms-client-flatten": true,
  + "$ref": "#/definitions/PowerBIWorkspaceLinkedServiceTypeProperties"
  + }
  + },
  + "required": [
  + "typeProperties"
  + ]
  + },
  + "PowerBIWorkspaceLinkedServiceTypeProperties": {
  + "description": "Power BI Workspace linked service properties.",
  + "type": "object",
  + "properties": {
  + "workspaceId": {
  + "type": "string",
  + "description": "The Power BI workspace id."
  + },
  + "tenantId": {
  + "type": "string",
  + "description": "The tenant id to which the Power BI workspace belongs."
  + }
  + },
  + "required": [
  + "workspaceId",
  + "tenantId"
  + ]
  }
  }
  }
  