Avoid duplicate ATTACH sent

[sacOO7]

• Attach related changes were introduced as a part of protocol 2.
• As per protocol 2, ATTACH msg should be sent for every channel in attaching, attached and suspended states once connected.
• There are various mechanisms by which duplicate ATTACH can be sent

1. ATTACH is added to the connection or global queue before being sent, check description on -> https://github.com/ably/ably-ruby/pull/416
2. ATTACH is sent periodically when channel is in SUSPENDED state as per https://sdk.ably.com/builds/ably/specification/main/features/#RTL13b.
3. In case of ably-java we had observed duplicate ATTACHED being received in the response during re-connection. Need to check if this is the case and how can we avoid it.

┆Issue is synchronized with this Jira Task by Unito

[sacOO7]

Proposed fix at https://github.com/ably/ably-java/pull/1052