Provide user preview for templated URLs outcomes

When adding a templated URL, a user may wish to see how one or more sample URLs would look when the template is applied in order to check that they have entered the template correctly and that the outcome is what they expect.

In order to achieve this we need to support:

• The user being able to set a list of URLs that should be used for this check/preview
• Backend support for returning the outcome of putting the set of sample URLs through the template
• UI for the user to be able to see the results of the templates being applied to the sample URLs

Previewing the outcome of applying a template should be possible in the UI no matter whether the template is for a Proxy, or is a Platform specific template