Add support for Pagy as pagination backend

[tpaulshippy]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Related Issue	#444
Need Doc update	yes

Describe your change

This change adds support for pagy as a pagination backend.

Co-authored by: Ryan Wolfe

What problem is this fixing?

Currently when using algolia with pagy, we have to use pagy_array which means that we are pulling the entire result set for every page. This is not optimal.

Here is a suggested addition to the README:

Even if we highly recommend to perform all search (and therefore pagination) operations from your frontend using JavaScript,
we support the following as pagination backends:
will_paginate
kaminari
pagy

---

pagy

To use :pagy, specify the :pagination_backend as follow:

AlgoliaSearch.configuration = { application_id: 'YourApplicationID', api_key: 'YourAPI', pagination_backend: :pagy }

Then, as soon as you use the search method, the returning results will be a paginated set:

# in your controller
@pagy, @posts = MyModel.search('foo', hitsPerPage: 10, page: params[:page] || 1)

# in your views
<%== pagy_nav(@pagy) %>

[DevinCodes]

Thank you for your contribution @tpaulshippy ! 🙇‍♂️

I have 2 nitpick comments about style, and one around the failing tests in the CI. Let me know if you have any questions!

[DevinCodes]

Suggested change

	raise(AlgoliaSearch::BadConfiguration, "AlgoliaSearch: Please add 'pagy' to your Gemfile to use pagy_search pagination backend")
	raise(AlgoliaSearch::BadConfiguration, "AlgoliaSearch: Please add 'pagy' to your Gemfile to use Pagy pagination backend")

[DevinCodes]

Some tests after this one are failing, because the pagination backend is configured globally by this line, and the return value differs from other pagination backends (others return one value, while pagy returns 2).

I see that Pagy defaults to returning 2 values (Pagy object and the paginated list of items), so we should reset the pagination backend after these tests have run to make the other tests still pass.

[DevinCodes]

Suggested change

	vars = {}
	vars[:count] = total_hits
	vars[:page] = options[:page]
	vars[:items] = options[:per_page]
	vars = {
	count: total_hits,
	page: options[:page],
	items: options[:per_page]
	}

[RyanJWolfe]

Hi @DevinCodes, thanks for the feedback, we have addressed your comments in the latest commit!

[DevinCodes]

The code looks good to me, thank you again for the contribution! I'll try to release this early next week 🙂

[DevinCodes]

This is released in the latest version! https://rubygems.org/gems/algoliasearch-rails/versions/2.3.2

Thank you again for the help on this 🙇