✨Add version to user-agent for AWS API calls

[aaroniscode]

What this PR does / why we need it:
The AWS SDK adds the SDK version to the user-agent of API calls. This adds the version of the Cluster API AWS provider to the user-agent string.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #1242

[aaroniscode]

For the reviewers -- note that because version information was needed for the controller (and not just clusterawsadm I refactored the version code to be a shared package for both to use.

I modeled the changes to the clusterawsadm version command to be very similar to how kubectl and kubeadm work.

Many thanks to @randomvariable for the assistance on the version refactoring.

[randomvariable]

/lgtm

[detiber]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aaroniscode, detiber

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[detiber]

/hold

[vincepri]

/hold cancel
/lgtm