Update UI help for template key field values in guided decision tables and guided rules

In the guided rule designer, whether guided rules, guided rule templates, guided rules with dsl, or in guided decision table designer (Add Column > Add condition BRL fragment (and action BRL fragment)), add some field in the embedded guided rule designer and then add a field value. Note that the value can be Literal, Template key, or Formula (and I think one other). Each value type has an info icon with help text, but the Template key (the most elusive) just repeats the Literal help text. See attached screen shot.

We really need to update the Template key help text to explain what template keys are and what they do. manstis@redhat.com has described it in detail in this BXMSDOC-2009 comment. I have also given a very basic note in our condition BRL fragment section (and action BRL frag section) of our new GDT doc for DM 7.0. I will remove the note(s) once the UI help text is in place.

This really should be worked out for DM 7.0, if at all possible. And it should't be something we need to document.