Update RecordType values for CNAME and MX examples (#13447)

Both examples 3 and 4 mention a RecordType of AAAA but should mention CNAME and MX respectively

Author: luisarnauth

src/PrivateDns/PrivateDns/help/New-AzPrivateDnsRecordConfig.md

@@ -127,7 +127,7 @@ This example creates a RecordSet named www in the private zone myzone.com. The r
 ```powershell
 PS C:\> $Records = @()
 PS C:\> $Records += New-AzPrivateDnsRecordConfig -Cname www.contoso.com
-PS C:\> $RecordSet = New-AzPrivateDnsRecordSet -Name "www" -RecordType AAAA -ResourceGroupName "MyResourceGroup" -TTL 3600 -ZoneName "myzone.com" -PrivateDnsRecords $Records
+PS C:\> $RecordSet = New-AzPrivateDnsRecordSet -Name "www" -RecordType CNAME -ResourceGroupName "MyResourceGroup" -TTL 3600 -ZoneName "myzone.com" -PrivateDnsRecords $Records
 
 Id                : /subscriptions/xxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/myresourcegroup/providers/Micros
                     oft.Network/privateDnsZones/myzone.com/CNAME/www
@@ -148,7 +148,7 @@ This example creates a RecordSet named www in the private zone myzone.com. The r
 ```powershell
 PS C:\> $Records = @()
 PS C:\> $Records += New-AzPrivateDnsRecordConfig -Exchange "mail.microsoft.com" -Preference 5
-PS C:\> $RecordSet = New-AzPrivateDnsRecordSet -Name "www" -RecordType AAAA -ResourceGroupName "MyResourceGroup" -TTL 3600 -ZoneName "myzone.com" -PrivateDnsRecords $Records
+PS C:\> $RecordSet = New-AzPrivateDnsRecordSet -Name "www" -RecordType MX -ResourceGroupName "MyResourceGroup" -TTL 3600 -ZoneName "myzone.com" -PrivateDnsRecords $Records
 
 Id                : /subscriptions/xxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/myresourcegroup/providers/Micros
                     oft.Network/privateDnsZones/myzone.com/MX/www