The change is very minor, it just extends the type definition for a feature implemented in #284 and thus fixes #332

I'm not a TS expert, so I'm happy for any input on this.

One minor point though: I'm not sure about tests. They are kind of broken for TS part right now and I fixed some small things (like mismatch in the engines / templates / extensions), but it is not possible, at least with ejs, to have one server serving both an application with a global template and an application with a route specific template, because these are mutually exclusive.

Another minor thing: in the template for index-with-no-data, there are some values specified, which are not optional for ejs. I can fix this, but I would like to discuss first how the fix should look like (e.g. running two fastify servers on different ports, one with global layout, one with local layout, updating templates accordingly or adding new ones etc.).

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct