refactor(go-forwarder): add client package

[ndakkoune]

What does this PR do?

Quick refactor to minimize future retry implementation scope by creating a client package

Motivation

Testing Guidelines

Additional Notes

I'll deal with the current state (kms/ssm/secretsmanager in config) when I will refactor at the end of the project.

Types of changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)
• This PR passes the unit tests
• This PR passes the installation tests (ask a Datadog member to run the tests)