feat: add hide_history_before option for adding members (#1645)

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## Description of the changes, What, Why and How?

When adding members to a channel, it is now possible to not only hide
all channel history for them (via hide_history), but also select a
timestamp in the past via hide_history_before. Any activity before that
will be hidden.

This PR adds an option to enable this feature.

## Changelog

- feat: add hide_history_before option for adding members

Author: Acconut

src/types.ts

@@ -331,6 +331,7 @@ export type ChannelAPIResponse = {
 
 export type ChannelUpdateOptions = {
   hide_history?: boolean;
+  hide_history_before?: string | Date;
   skip_push?: boolean;
 };