Document the new net/grpc's authority param

Author: mstoykov

docs/sources/k6/next/javascript-api/k6-net-grpc/params.md

@@ -13,6 +13,7 @@ _Params_ is an object used by the gRPC methods that generate RPC requests. _Para
 
 | Name                            | Type            | Description                                                                                                                                                                                                                                                              |
 | ------------------------------- | --------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
+| `Params.authority`              | string          | Specifies the value of the :authority pseudo-header and as the server name in authentication handshake. If missing this is derived from the hostname.                                                                                                                    |
 | `Params.discardResponseMessage` | boolean         | Specify if response messages should be discarded. This reduces the amount of memory required, and the amount of garbage collection, which reduces the load on the testing machine and can help produce more reliable test results. Default is `false`.                   |
 | `Params.metadata`               | object          | Object with key-value pairs representing custom metadata the user would like to add to the request. Values of [keys ending with `-bin`](https://grpc.io/docs/what-is-grpc/core-concepts/#metadata) will be treated as binary data.                                       |
 | `Params.tags`                   | object          | Key-value pairs where the keys are names of tags and the values are tag values. Response time metrics generated as a result of the request will have these tags added to them, allowing the user to filter out those results specifically, when looking at results data. |