Split aws propagator out of instrumentation

[thompson-tomo]

Currently we have the aws-sdk instrumentation which generates spans & also includes a propagator which is only used for messaging.

We should look to either:

• split the propagator out into it's own gem & also introduce an aws_messaging instrumentation gem which just adds the propagator to the aws sdk for v4.
• introduce just aws_messaging instrumentation gem which contains the propagator.

My preference is the first option as we could reuse the propagator within the sdk gem, we could request for aws sdk to natively support propagation paving path to deprecating instrumentation gem.

Reason to make this change is that it enables us to restrict the current sdk gem to just v2 & v3 while also freezing development of it.

[github-actions]

👋 This issue has been marked as stale because it has been open with no activity. You can: comment on the issue or remove the stale label to hold stale off for a while, add the keep label to hold stale off permanently, or do nothing. If you do nothing this issue will be closed eventually by the stale bot.