Add role_id as an alias name source for AWS and change the defaults

[jefferai]

No description provided.

[jefferai]

@vishalnayak I .... did not mean to merge this. Rather than force-push back, can you just review after-the-fact?

[vishalnayak]

LGTM!

[joelthompson]

@jefferai -- I'm not entirely certain that this will do as the entry in the changelog says. In particular, the changelog entry states, "Existing mounts will not be affected." However, I believe this can affect existing mount points. identityConfigEntry in path_config_identity.go is where the default values are added; however, an updated config entry with the default values is never written back to storage. So, if a user has never set the identity config of a mount, then before upgrading, logins would get identity aliases corresponding to identityAliasIAMUniqueID and identityAliasEC2InstanceID, while after upgrading, logins would get identity aliases of the role ID. Right? This might be fine as a breaking change, fixing it would probably require versioning the identityConfig struct along with an upgrade path, and I'm not sure it's worth the added complexity versus just calling something out in the changelog with instructions on how to opt back in to the old behavior if people cared.