support kubectl annotate

[michael-db]

What would you like to be added:
Support an "Annotate" task (with overwrite default) in addition to "Apply".

Why is this needed:
kubectl apply might suffice for adding an annotation if the yaml of the resource was available - but kudo also seems to offer no way to get the yaml of an existing resource: it assumes that the only resources you ever want to touch are those which the operator is creating, i.e., where you already have the yaml.

If there is some workaround, it's not obvious. As things stand, it looks like I need to create an operator-sdk program just for a very simple task of adding an annotation to an existing resource.