Make paginator paging params configurable

[AMHOL]

Similar to #188 but maintains backwards compatibility as requested.

Param keys can be configured with:

JsonApiClient::Paginating::Paginator.configure do |config|
  config.page_param = "page[number]"
  config.per_page_param = "page[size]"
end

This PR adds a dependency on dry-configurable, I can remove this and implement it using plain old Ruby if desired.

[chingor13]

Yeah, I'd rather not add an additional dependency for something that isn't that complex. There's already an established convention of using class_attribute for configuration.

The downside of the class_attribute config for the default paginator class is the case of 2 separate apis that have different pagination rules wouldn't both be able to use the same paginator class. In any case, I'm not sure that the dry-configurable gem would handle that scenario.

[AMHOL]

@chingor13 updated as requested

[chingor13]

Thanks!

[AMHOL]

Thanks for merging 😄