Add json output to install and related commands

[adleong]

We add support for the --output/-o flag in linkerd install and related commands. The supported output formats are yaml (default) and json. Kubectl is able to accept both of these formats which means that the output can be piped into kubectl regardless of which output format is used.

The full list of install related commands which we add json support to is:

• linkerd install
• linkerd prune
• linkerd upgrade
• linkerd uninstall
• linkerd viz install
• linkerd viz prune
• linkerd viz uninstall
• linkerd multicluster install
• linkerd multicluster prune
• linkerd multicluster uninstall
• linkerd jaeger install
• linkerd jaeger prune
• linkerd jaeger uninstall