feat: support members_template property for campaigns (#1647)

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- [ ] Code changes are tested

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

The campaign API recently added support for a new property
members_template that can be used as an alternative to members. Its
benefit is that the client is also able to define the channel role and
custom data for members that are added to newly created channels for
campaigns.

## Changelog

- feat: support members_template property for campaigns

Author: Acconut

src/types.ts

@@ -3155,6 +3155,11 @@ export type CampaignData = {
     custom?: {};
     id?: string;
     members?: string[];
+    members_template?: Array<{
+      user_id: string;
+      channel_role?: string;
+      custom?: Record<string, unknown>;
+    }>;
     team?: string;
   };
   create_channels?: boolean;