Support adding to the pages to be visited in build time render during build time render

[matt-gadd]

Enhancement
With blocks, it's now possible to discover content at build time rendering (ie reading a number of markdown files in a directory), this might mean that we want to then visit routes to get output from too. This is not currently possible due to the build time render paths being static in the dojorc. It'd be nice if it would be possible to dynamically add to those paths when running in build time rendering

[agubler]

@matt-gadd Is this something that we still need even with the new auto discovery capabilities? They are different, as you could perhaps add a route that is not discoverable via the rendered application.