Add AuditEnabled to EXOSharedMailbox

[JuliusRauschen]

Pull Request (PR) description

This PR adds AuditEnabled to EXOSharedMailbox

This Pull Request (PR) fixes the following issues

None

Task list

• Added an entry to the change log under the Unreleased section of the file CHANGELOG.md.
  Entry should say what was changed and how that affects users (if applicable), and
  reference the issue being resolved (if applicable).
• Resource parameter descriptions added/updated in the schema.mof.
• Resource documentation added/updated in README.md.
• Resource settings.json file contains all required permissions.
• Examples appropriately added/updated.
• Unit tests added/updated.
• New/changed code adheres to DSC Community Style Guidelines.

[NikCharlebois]

-PropertySets is not a valid property for the Get-Mailbox cmdlet. What are we trying to accomplish with this PR?

[JuliusRauschen]

I mistakenly added -PropertySets All to Get-Mailbox as I confused it with Get-EXOMailbox. I am not very experienced with Powershell yet, so I am sorry for the inconvenience. Thanks for your understanding!

[FabienTschanz]

@NikCharlebois LGTM.