Version field for kapp app annotations

**Describe the problem/challenge you have**

`kapp`'s app deployments track the app's name, but do not record any _version_ for the deployment to show in `kapp list` etc.

While it is possible to use `ytt`, `kustomize`'s `commonAnnotations` etc to inject a `kubernetes.io/version` annotation into deployed resources, `kapp` doesn't know to look for it, and no version can be shown in `kapp list`. It would be immensely useful if `kapp list` provided an at-a-glance view of deployed component versions.

See fluxcd's `flux get kustomization`, Helm's `helm list` for other tools that present at-a-glance component version information.

**Describe the solution you'd like**

It would be very helpful if `kapp deploy` took an optional application version flag, which could also be injected as a kapp config stanza. This version would appear in `kapp list`.

kapp config could also be added that propagates the supplied version to `kubernetes.io/version` annotations on all components kapp is deploying. This should probably be off by default for compatibility reasons.

**Anything else you would like to add:**

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