Catzilla

This PR changes `UpdateSubscriberPreferencesOptions` struct to valid request body format Field types in that struct changed to pointers, to avoid bug with `omitempty` tag, as described in issue #90 Added...

According to [API Reference](https://docs.novu.co/api-reference/subscribers/update-subscriber-preference) for `UpdatePreferences` method, `channel` field should be object, not array Moreover, this endpoint supports partial update, which means that only `enabled` or only `channel` may be...

According to [API Reference](https://docs.novu.co/api-reference/subscribers/mark-a-subscriber-feed-message-as-seen) for `MarkMessageSeen` method, `seen` and `read` fields should be inside `mark` object This PR changes `SubscriberMarkMessageSeenOptions` struct to valid request body format Fixes #88

According to [API Reference](https://docs.novu.co/api-reference/subscribers/mark-a-subscriber-feed-message-as-seen) for `MarkMessageSeen` method, `seen` and `read` fields should be inside `mark` object