Version field in AWSLaunchTemplate spec is missing comments/validation

[randomvariable]

/kind feature
/help
/good-first-issue

Describe the solution you'd like
[A clear and concise description of what you want to happen.]

Add validation and/or comments to version field in AWSLaunchTemplate spec

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• Cluster-api-provider-aws version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

[k8s-ci-robot]

@randomvariable:
This request has been marked as suitable for new contributors.

Please ensure the request meets the requirements listed here.

If this request no longer meets these requirements, the label can be removed
by commenting with the /remove-good-first-issue command.

In response to this:

/kind feature
/help
/good-first-issue

Describe the solution you'd like
[A clear and concise description of what you want to happen.]

Add validation and/or comments to version field in AWSLaunchTemplate spec

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• Cluster-api-provider-aws version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[randomvariable]

Broken out of #1968