Update Key Vault Secrets README (Azure#2047)

* init README for official keyvault secrets crate

* Updated formatting and samples

* Update README with new SecretClient usage and example code

* Refactor README to improve SecretClient usage instructions and examples

* Added examples for update, delete and delete&purge

* Added list secrets example

* Removed separate section for async examples

* KeyVault doesn't allow for "_" in secret names so all sample secret names have been switched from secret_name to secret-name

* Updated troubleshooting section

* Removed next steps section as we have no example files yet

* removing unused links

* Changed "Secrets" -> "secrets"

* Fix formatting in README.md for Key Vault secret description

* Refactor README.md for Key Vault secrets: update code snippets, correct parameter names, and improve clarity

* Udpated examples to be simpler

* Updated troubleshooting readme

* Updated list secrets example and removed delete and purge example

* Fixed broken links and removed additional docs section. Will add back when the additional docs actually exist.

* Adding Heath's suggestion on text for delete secret example

* updated deleted secret example text with Heath's new suggestion

* Update `delete_secret` description.

* Clone credentials as best practice

---------

Co-authored-by: Heath Stewart <[email protected]>

Author: ronniegeraghty