feat: Add `Twilio::HTTP::Client#configure_connection`

[darwinShopify]

Add the configure_connection method to the Twilio::HTTP::Client class to allow consumers to apply custom configuration to the Faraday connection.

The motivation for this change is to allow consumers to register custom middleware.

Checklist

• [x] I acknowledge that all my contributions will be made under the project's license
• [x] I have made a material change to the repo (functionality, testing, spelling, grammar)
• [x] I have read the Contribution Guidelines and my PR follows them
• [x] I have titled the PR appropriately
• [x] I have updated my branch with the main branch
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have added the necessary documentation about the functionality in the appropriate .md file
• [ ] I have added inline documentation to the code I modified

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.

[darwinShopify]

@JenniferMah updated and ready to go!