[V2] Add encryption support to realtime channels

[sacOO7]

• Based on https://github.com/ably/ably-go/pull/603
• Need to be done in a separate branch V2 since this is a possible breaking change => https://github.com/ably/ably-go/issues/608
• Additional publish-subscribe type safety implementation suggested => https://github.com/ably/ably-go/issues/584
• Link to internal discussion -> https://ably-real-time.slack.com/archives/C030C5YLY/p1689930453333929

┆Issue is synchronized with this Jira Task by Unito

[sync-by-unito[bot]]

➤ Automation for Jira commented:

The link to the corresponding Jira issue is https://ably.atlassian.net/browse/SDK-3766