Spec alignement for presence message extras

[ikurek]

This task is required for https://github.com/ably/ably-flutter/issues/128

According to the spec, presence methods should support additional extras parameter. Related spec items are:

• https://docs.ably.io/client-lib-development-guide/features/#TP3i
• https://docs.ably.io/client-lib-development-guide/features/#RTP8e
• https://docs.ably.io/client-lib-development-guide/features/#RTP9a
• https://docs.ably.io/client-lib-development-guide/features/#RTP10a

And methods that should be updated are:

• presence.enter
• presence.update
• presence.leave
• presence.enterClient
• presence.updateClient
• presence.leaveClient

┆Issue is synchronized with this Jira Story by Unito

[QuintinWillison]

Looks like a duplicate of https://github.com/ably/ably-java/issues/736.