Support dynamic template selection

[bobh66]

What problem are you facing?

I have a need to use different templates for the same composition depending on user input. The existing implementation only supports a hard-coded template name reference which must be specified when the Composition is created.

How could this Function help solve your problem?

Allow for the template name to be determined based on content of the composite resource, similar to the discussion in crossplane/crossplane#5906

This could mean specifying a template name from a composite field source, or using dynamic label selection to select a configmap template based on label keys and values, where the values could also come from the composite.