Split MessageResolver and Ktor support to different module

[ageorgousakis]

Is your feature request related to a problem? Please describe.
It would be better to split MessageResolver and key generators to a separate module which does not require Ktor dependencies so that someone can use it without Ktor or add it as a dependency to a module that does not require Ktor.

Ktor plugin can be in another module with the dependencies needed from Ktor project

Describe the solution you'd like
Split library to two modules, one for message resolver and one for Ktor support

Describe alternatives you've considered
I cannot think any other alternative