Implement presence re-entry requirement change for 1.1

[paddybyers]

See ably/docs#711

Related: #163

Acceptance criteria:
After confirming that the lib satisfies the new RTP17c, please update the spec spreadsheet accordingly

┆Issue is synchronized with this Jira Bug by Unito

This is implemented. Members are re-entry in two cases: in_sync state (RTP17c1) and sync_none (RTP17c2)
In both situations the following method is responsible for automatic re-entry:

ably-ruby/lib/ably/realtime/presence/members_map.rb

Line 270 in d901e96

def re_enter_local_member_missing_from_presence_map(presence_message)

RTP17c, RTP17c1
https://github.com/ably/ably-ruby/blob/main/lib/ably/realtime/presence/members_map.rb#L248 -> https://github.com/ably/ably-ruby/blob/main/lib/ably/realtime/presence/members_map.rb#L264

RTP17c, RTP17c2
https://github.com/ably/ably-ruby/blob/main/lib/ably/realtime/channel/channel_manager.rb#L39 ->
https://github.com/ably/ably-ruby/blob/main/lib/ably/realtime/channel/channel_manager.rb#L260 ->
https://github.com/ably/ably-ruby/blob/main/lib/ably/realtime/presence/presence_manager.rb#L58 ->
https://github.com/ably/ably-ruby/blob/main/lib/ably/realtime/presence/members_map.rb#L238 -> https://github.com/ably/ably-ruby/blob/main/lib/ably/realtime/presence/members_map.rb#L244 -> https://github.com/ably/ably-ruby/blob/main/lib/ably/realtime/presence/members_map.rb#L248