Issue 246 auth backend

[JadeKharats]

WHAT is this pull request doing?

Allows ConnectionFactory to use a chain of responsibility to authenticate users via multiple configured providers. A cache management is implemented to avoid calls that are too slow in http

WIP :
Initialize auth_chain with config.
Find a solution so that external auth services return LavinMQ::User

HOW can this pull request be tested?

Added fake auth_http_backend server in helper.
Cache and auth_chain have dedicated tests

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[JadeKharats]

I have read the CLA Document and I hereby sign the CLA

[kickster97]

Awesome!
I need access/rights to the fork repository in order to cherry pick code into the Oauth2 branch

[kickster97]

Closing this because we now have #956 :)