Unregister-SecretVault should be ConfirmImpact "High"

[JustinGrote]

It is common a user may be pipelining unregistrations, so commands like Get-SecretVault | Unregister-SecretVault which can unregister a ton of vaults should not be allowed to happen without at least some sort of confirmation

[SydneyhSmith]

Thanks @JustinGrote we made this choice to follow the pattern of other Unregister cmdlets in PowerShell (like scheduled jobs), and because it does not necessarily remove the underlying vault, however we will leave this open for discussion