[maven plugin] Make serializer optional in client generation

[vsahav]

Is your feature request related to a problem? Please describe.
The graphql maven/gradle plugin would suit a wider array of uses if it would be possible to opt-out from serialization (serializer annotations on generated models) all-together or having the ability to provide a custom fully qualified name for the annotation to use. Custom client implementations might not rely on either Jackson or kotlinx.

Describe the solution you'd like
A expansion of the serializer enum to include a option "NONE" or equivelant that would leave the models without any serializer related annotations. Alternatively a mechanism to supply your own annotation.