Extract HTTP client logic to HttpClient and JavaHttpClient. Make Http…

[githubmicrob]

…Client configurable.

Summary

Extracted HTTP client functionality to separate class. Introduced HttpClient interface to make the implementation of HTTP client replaceable. In our case having another implementation is necessary because Java implementation doesn't work with HTTPS proxies.

Fix: braintree/braintree_java#135

Checklist

• [x] Added changelog entry
• [x] Ran unit tests (rake test:unit)
• [x] I understand that unless this is a Draft PR or has a DO NOT MERGE label, this PR is considered to be in a deploy ready state and can be deployed if merged to main

[ishestakov]

Hello @saralvasquez, Hope you can advice what should be the process of this PR🙏. Seems it will allow to use Braintree java sdk behind https proxy