Allow not having to set values for Helm release

[jpds]

I sometimes just want to deploy a helm release without having to set any values outside of the defaults, however flux doesn't allow me to do this.

[squaremo]

As in, it requires a values: section in the HelmRelease manifest?

[jpds]

@squaremo Yes.

[stefanprodan]

A workaround is to use values: {}

[squaremo]

I suppose we should alter the OpenAPI schema so values isn't required (and make sure the code doesn't balk if it's absent).