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.
• suspended state is partially implemented and need to be fully implemented. Related -> Inconsistent codebase state around whether SUSPENDED channel state is implemented #568
• 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 -> [ECO-4687][Protocol-2] Fix duplicate outgoing ATTACH msg ably-pubsub-ruby#416
2. ATTACH is sent periodically when channel is in SUSPENDED state as per https://sdk.ably.com/builds/ably/specification/main/features/#RTL13b. In case of ably-go, ATTACH is sent periodically when it is in DETACHED state ( since SUSPENDED is not fully implemented ). Timers sending ATTACH periodically can cause duplicate ATTACH being sent on CONNECTED

┆Issue is synchronized with this Jira Task by Unito