Add in a hook for supplying variables for template render

[linsword13]

This is used as the basis to allow workflow manager to provide a set of variables for all its register_template directives.

[douglasjacobsen]

How should we think about this if we want different templates to have different variables that they render with?

[linsword13]

How should we think about this if we want different templates to have different variables that they render with?

Yeah for that we still have the extra_vars and extra_vars_func arguments via the register_template. And those have higher precedence over this template_render_vars.

[douglasjacobsen]

OK, thanks!