Fix boosted category facet in Resource model.

We recently added a boosted category column on the services table, with
the intent of syncing it to Algolia so that we can perform special types
of search ranking based on it on the frontend. However, the way we added
it resulted in an obscure bug where the feature appeared to work until
someone visits the edit page and saves an edit to a resource or service.

The issue is that when we set the `attributesForFaceting` property, we
only added the `boosted_category` field to the Service model, not the
Resource model. Since we're doing something unusual by sharing the same
index for both the Service and Resource model, what actually happens is
that the Resource model would sometimes override the
`attributesForFaceting` in the Algolia index with its own list, causing
that attribute to not be usable in filtering anymore.

This fixes the issue by adding the `boosted_category` field to
Resource's list of facets. To prevent this kind of issue from happening
in the future, we refactor the list of attributes for faceting into a
single constant that both the Service and Resource models share.

app/models/resource.rb

@@ -44,7 +44,7 @@ class Resource < ActiveRecord::Base
                   index_name: "#{Rails.configuration.x.algolia.index_prefix}_services_search",
                   id: :algolia_id do
       # specify the list of attributes available for faceting
-      attributesForFaceting %i[categories open_times eligibilities associated_sites type]
+      attributesForFaceting Rails.configuration.x.algolia.attributes_for_faceting
       # Define attributes used to build an Algolia record
       add_attribute :_geoloc do
         if addresses&.any?

app/models/service.rb

@@ -38,7 +38,7 @@ class Service < ActiveRecord::Base
                   index_name: "#{Rails.configuration.x.algolia.index_prefix}_services_search",
                   id: :algolia_id do
       # specify the list of attributes available for faceting
-      attributesForFaceting %i[categories open_times eligibilities associated_sites type boosted_category]
+      attributesForFaceting Rails.configuration.x.algolia.attributes_for_faceting
 
       # Default has "geo" before "filters", but we need it after if we want
       # optional filters to have higher priority than distance.

config/application.rb

@@ -24,6 +24,12 @@ class Application < Rails::Application
       config.x.algolia.index_prefix.present?
     ].all?
 
+    # Attributes for faceting (filtering, sorting, etc.) in Algolia. This needs
+    # to be kept in sync between the Service and Resource models, since we're
+    # doing something unusual by having them share the same index, so we define
+    # the list of attributes for faceting as a single constant here.
+    config.x.algolia.attributes_for_faceting = %i[categories open_times eligibilities associated_sites type boosted_category]
+
     config.x.airtable.api_key = ENV['AIRTABLE_API_KEY']
 
     config.x.google.api_key = ENV['GOOGLE_API_KEY']