Add Azure auth method

[Ramesh7]

This PR is about adding the Azure Auth method as described here :
https://www.vaultproject.io/docs/auth/azure#via-the-api

[hashicorp-cla]

Thank you for your submission! We require that all contributors sign our Contributor License Agreement ("CLA") before we can accept the contribution. Read and sign the agreement

Learn more about why HashiCorp requires a CLA and what the CLA includes

---

Ramesh Sencha seems not to be a GitHub user.
You need a GitHub account to be able to sign the CLA. If you already have a GitHub account, please add the email address used for this commit to your account.

_{Have you signed the CLA already but the status is still pending? Recheck it.}

[ssethi19]

Hi,

Can you provide the status of this PR?

[dhuckins]

@Ramesh7 can you sign the CLA (see bot comment for details) and pull down the latest? we just made some CI changes

thanks!