Vault backend for Consul ACL bootstrapping in AWS

[copernicium-112]

Vault as backend for consul ACL bootstrapping or and support ASG scaling with ACL configured
This module is super helpful for us. we are trying to leverage this module in production and spun up consul, nomad clusters.
But right now there is no support to enable ACL while we provision consul servers/clients behind an ASG.
It will be nice to have vault as ACL backend since Vault has AWS auth methods to interact with

We can also see a Open PR having AWS SSM as backend but still its yet to be reviewed and merged. -> do we know whether this is preferred over the vault.