message: [Web] Add Swagger for Service Principal
diff: "description": "Web activity authentication properties.",
  "properties": {
  "type": {
  - "description": "Web activity authentication (Basic/ClientCertificate/MSI)",
  + "description": "Web activity authentication (Basic/ClientCertificate/MSI/ServicePrincipal)",
  "type": "string"
  },
  "pfx": {
  - "description": "Base64-encoded contents of a PFX file.",
  + "description": "Base64-encoded contents of a PFX file or Certificate when used for ServicePrincipal",
  "$ref": "../datafactory.json#/definitions/SecretBase"
  },
  "username": {
  - "description": "Web activity authentication user name for basic authentication.",
  + "description": "Web activity authentication user name for basic authentication or ClientID when used for ServicePrincipal",
  "type": "string"
  },
  "password": {
  - "description": "Password for the PFX file or basic authentication.",
  + "description": "Password for the PFX file or basic authentication / Secret when used for ServicePrincipal",
  "$ref": "../datafactory.json#/definitions/SecretBase"
  },
  "resource": {
  "description": "Resource for which Azure Auth token will be requested when using MSI Authentication.",
  "type": "string"
  + },
  + "userTenant": {
  + "description": "TenantId for which Azure Auth token will be requested when using ServicePrincipal Authentication. Type: string (or Expression with resultType string).",
  + "type": "object"
  }
  },
  "required": [
  