Option to generate npm pacakges with package.json version matching smithy/aws-sdk client versions

[everett1992]

Even with the recent changes to codegen to produce clients that depend on ^ ranges, it's a good idea to match the version of all the clients a consumer depends on. @aws-sdk/ clients are published together, so it's easy to match @aws-sdk/clients-s3 and @aws-sdk/clients-ec2.

I'd like an option in smithy-build.json to set the generated package.json version matching the smithy/aws-sdk ecosystem.
I've been implementing this feature in my own packages with a script that updates the version based on the version of @aws-sdk/types, but it's not going to be accurate.

          "packageJson": {
	            "scripts": {
	              "prepare": "npm pkg set version=$(npx -y semver -c \"$(npm pkg get 'dependencies.@aws-sdk/types')\")"
	            }
	          }

Another part of this feature request that I haven't solved myself is how to version model changes when there haven't been any codegen changes. I'd still want the version to be close to smithy's, and I wouldn't want it to conflict with future smithy versions.
I think I could use a timestamp for the patch version.