[ECO-4686] Implement internal presence

[sacOO7]

• Fixed [ably-ruby][no-connection-serial] Implement missing internal presence #392

Commit summary

• renamed :in_sync enum to :sync_completed, since :in_sync is a very confusing term and doesn't go as per spec.
• removed resume_sync_proc code that does client initiated sync when channel attaches with has_presence flag. This doesn't go as per spec.
• added on_attach method to presence_manager that

1. start or end sync depending on has_presence flag
2. enter local members when on_attach method is called.

• Added a new enter_client_with_id method to presence that enters local members with id. Earlier local members were entered at the end of the sync and didn't support entering members with given id.

[sacOO7]

Closing in favor of #410