fix(CLI): Print specific command when prompting to install the Gateway API

[adleong]

If the user runs linkerd install --crds when the Gateway API CRDs are not already present on the cluster, Linkerd will print an error prompting the user to first install the gateway API.

To make this a more streamlined user experience, we update the message to include a specific command for installing the Gateway API instead of merely linking to the Gateway API documentation.

> linkerd install --crds                                                                                     
The Gateway API CRDs must be installed prior to installing Linkerd. Run:

kubectl apply -f https://github.com/kubernetes-sigs/gateway-api/releases/download/v1.2.1/standard-install.yaml

or see https://gateway-api.sigs.k8s.io/guides/#installing-gateway-api for more options.