feature/AKD-187: Added Azure 'Web Apps Backup Retention Period' Plugin and test cases

[ali-imran7]

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

:white_check_mark: AkhtarAmir
:x: ali-imran7
_{You have signed the CLA already but the status is still pending? Let us recheck it.}