Enable soft delete and resource locks on keyvault

[SudhakaraReddyEvuri-zz]

Description

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate change log has been updated
• The PR does not introduce breaking changes
• If applicable, the changes made in the PR have proper test coverage
• For public API changes to cmdlets:
  • the changes have gone through a cmdlet design review
  • the cmdlet markdown files were generated using the platyPS module

[SudhakaraReddyEvuri-zz]

These changes to AzureDiskEncryption pre-requisites sample script enable soft delete and add resource lock on KeyVault . This will show an example on how to prevent accidental deletion of encryption secrets in customers key vault.

[cormacpayne]

@SudhakaraReddyEvuri what kind of validation is done around this script? I remembered we previously talked about having this script tested in some fashion, we just want to ensure that the functionality being added is being tested and validated

[cormacpayne]

@SudhakaraReddyEvuri as a general note, I think it would be nice if we added a #requires statement at the top of this file so users know they need modules outside of AzureRM.Compute to run this script (such as AzureRM.KeyVault and AzureRM.Resources). This will prevent users from getting into the situation where the script fails because it cannot find a cmdlet rather than failing instantly because they don't have all of the necessary modules on their machine.