Add Go AzureIdentityCredentialAdapter, readme and test (jongio#32)

* add go etension

* add go model

* add go model

* change readme

* change code

* change code and readme

* change readme

* change according to comment

* refactor with base adapter

* remove comment code

* change according to comments

* change according to comments

* change readme

* change according to comments

* change according to comments

* change according to comments

* change package version

Co-authored-by: Zhanle Tu <[email protected]>