Populate empty proxy-version annotation

[jeremychase]

Set proxy-version annotation to LinkerdVersion when image version is the empty string.

Tested when installed via CLI:

$ k get po -o yaml -n emojivoto | grep proxy-version
      linkerd.io/proxy-version: dev-0911ad92-jchase
      linkerd.io/proxy-version: dev-0911ad92-jchase
      linkerd.io/proxy-version: dev-0911ad92-jchase
      linkerd.io/proxy-version: dev-0911ad92-jchase

Untested when installed via Helm.

Addressing: #9311

Signed-off-by: Jeremy Chase [email protected]

[adleong]

I think it would be also good to get rid of where the CLI unnecessarily populates this value here: https://github.com/linkerd/linkerd2/blob/main/pkg/charts/linkerd2/values.go#L247

This makes the behavior more consistent between Helm and the CLI.