Dynamic Route Rule

**Is your feature request related to a problem? Please describe.**
https://github.com/kataras/iris/issues/1507

**Describe the solution you'd like**
I need to dynamically modify the runtime routing, including request paths, request middleware, request handlers, and possibly add/remove a routing rule dynamically, because I want to build a gateway service with iris

**Describe alternatives you've considered**
We have thought about using middleware to deal with these contents, but it is not reasonable. At present, the whole gateway is based on gin. However, we may need to consider other ways to achieve our requirements due to the above problems

**Additional context**
Add any other context or screenshots about the feature request here.