release: builld cloud/vm/oci images if explicitly requested

[kevans]

Summary

The knobs are useful to have to control what make release does by
default, but it's also quite possible to just drive individual targets
if you don't plan to generate the entire set of release images. Instead
of forcing the WITH_* knobs to be set there, just assume it's implied if
these individual targets were explicitly requested.

Sponsored by: Klara, Inc.

[cperciva]

When you get to cloudware, my sense is that it's more likely someone will run e.g. make ec2ami-desktop-ufs rather than make cloudware-release.

Perhaps a better solution would be to have the relevant Makefile logic included unconditionally and have the WITH_* flags only control which targets are dependencies of release ?