Refactor all query config stuff into separate classes and added specs

...controllers/projects/cycle_analytics/events_controller.rb

app/serializers/entity_date_helper.rb

lib/gitlab/cycle_analytics/base_config.rb

lib/gitlab/cycle_analytics/code_config.rb

lib/gitlab/cycle_analytics/events_fetcher.rb

lib/gitlab/cycle_analytics/events_query.rb

lib/gitlab/cycle_analytics/issue_config.rb

lib/gitlab/cycle_analytics/plan_config.rb

lib/gitlab/cycle_analytics/production_config.rb

lib/gitlab/cycle_analytics/query_config.rb

lib/gitlab/cycle_analytics/review_config.rb

lib/gitlab/cycle_analytics/staging_config.rb

lib/gitlab/cycle_analytics/test_config.rb

spec/lib/gitlab/cycle_analytics/code_config_spec.rb

spec/lib/gitlab/cycle_analytics/events_spec.rb

spec/lib/gitlab/cycle_analytics/issue_config_spec.rb

spec/lib/gitlab/cycle_analytics/plan_config_spec.rb

spec/lib/gitlab/cycle_analytics/production_config_spec.rb

spec/lib/gitlab/cycle_analytics/review_config_spec.rb

spec/lib/gitlab/cycle_analytics/shared_config_spec.rb