[QL] Refactor Spike for Multiple v1/config calls

[KunJeongPark]

Summary of changes

• Recreate merchant integration that instantiates BTAPIClient on button press along with Payment Method Client instantiation
• Inject config object into BTAnalyticsService to avoid additional v1/config calls

Checklist

• [ ] Added a changelog entry

Authors

List GitHub usernames for everyone who contributed to this pull request.

• @KunJeongPark @richherrera

[KunJeongPark]

I will write a test that fails against https://github.com/braintree/braintree_ios/pull/1333/commits/2a2bf1e5c17d265f45f427471540e728b9ba8532 before I made changes on for config injection to BTAnalyticsService.

It should still fail since there is still duplication.

Plan is to create ConfigurationLoader per Sammy's suggestion and incorporate elements of previous PR on Investigate triple v1/config call ticket, where I addressed a possible solution for multiple calls in some scenarios, in the ConfigurationLoader. https://github.com/braintree/braintree_ios/pull/1308