allow defining clients on initialization

[mstate]

We needed to use vendor provideded SSL certificates to make calls to multiple domains from Async::HTTP::Internet. Unfortunately, the options that you can pass in are only for a single URL. To allow for our use case, we need to define url => Async::HTTP::Client outside of our Async::HTTP::Internet.new call and pass them in as an argument.

Types of Changes

• New feature.
• Updated documentation.

Contribution

• I added tests for my changes.
• I tested my changes locally.
• I agree to the Developer's Certificate of Origin 1.1.