[KeyVault] Supported accepting rotation policy in a JSON file

[BethanyZhou]

Description

Added two parameter sets to support accepting rotation policy in a JSON file:

   Set-AzKeyVaultKeyRotationPolicy [-VaultName] <string> [-Name] <string> -PolicyPath <string> [-DefaultProfile
    <IAzureContextContainer>] [-WhatIf] [-Confirm] [<CommonParameters>]

    Set-AzKeyVaultKeyRotationPolicy [-InputObject] <PSKeyVaultKeyIdentityItem> -PolicyPath <string> [-DefaultProfile
    <IAzureContextContainer>] [-WhatIf] [-Confirm] [<CommonParameters>]

Two breaking changes are allowed by Damien and Dingmeng

Checklist

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• The title of the PR is clear and informative
• The appropriate ChangeLog.md file(s) has been updated:
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• 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:
  • a cmdlet design review was approved for the changes in this repository (Microsoft internal only)
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  • the markdown help files have been regenerated using the commands listed here