Use V3 Pact interface

[YOU54F]

Currently we use the pact js v2 interface, and so can only generate version 2.0.0 spec files.

Would be good to use pact js v3 interface, and ideally v4 too, for all the juicy pact plugin goodness, and multi protocol contracts.

#23 is a gnarly effort with much code duplication, hopefully it serves as inspiration for someone to do it in a nicer way.

Demo here

https://github.com/YOU54F/nestjs-pact-test#based-on-v3-pact-specification-and-pact-js-v3-interface

[YOU54F]

Closing due to lack of interest, happy for willing contributors to implement the changes if required 👍🏾