Security insights module New-AzSentinelAlertRule EntityMapping Parameter wrong Type

### Description

I'm working on deploying analytic rules using powershell i have more that one entity type in some rules and more than field mapping in other. The problem is that it accept only HashTables with one Type and one Field mapping.

### Issue script & Debug output

```PowerShell
EntityMapping = @(
@{
EntityType = "Account"
FieldMapping = @(
@{
Identifier = "FullName"
ColumnName = "AccountDisplayName"
},
@{
Identifier = "AadUserId"
ColumnName = "AccountObjectId"
}
)
}
)
```

### Environment data

```PowerShell
Name Value
---- -----
PSVersion 5.1.22000.1335
PSEdition Desktop
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0...}
BuildVersion 10.0.22000.1335
CLRVersion 4.0.30319.42000
WSManStackVersion 3.0
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1
```

### Module versions

```PowerShell
Script 3.0.1 Az.SecurityInsights {Get-AzSentinelAlertRule, Get-AzSentinelAlertRuleAction, Get-AzSentinelAlertRuleTemplate, Get-AzSentinelAutomationRule...}
```

### Error output

```PowerShell
Message : An error occurred while creating the Azure Sentinel alert rule: Cannot process argument
transformation on parameter 'EntityMapping'. Cannot convert the "System.Object[]" value of type
"System.Object[]" to type
"Microsoft.Azure.PowerShell.Cmdlets.SecurityInsights.Models.Api20210901Preview.EntityMapping".
StackTrace :
Exception : Microsoft.PowerShell.Commands.WriteErrorException
InvocationInfo : {rules.ps1}
Line : .\rules.ps1
Position : At line:1 char:1
+ .\rules.ps1
+ ~~~~~~~~~~~
HistoryId : 2

Message : Cannot process argument transformation on parameter 'EntityMapping'. Cannot convert the
"System.Object[]" value of type "System.Object[]" to type
"Microsoft.Azure.PowerShell.Cmdlets.SecurityInsights.Models.Api20210901Preview.EntityMapping".
StackTrace : at System.Management.Automation.ExceptionHandlingOps.CheckActionPreference(FunctionContext
funcContext, Exception exception)
at lambda_method(Closure , Object[] , StrongBox`1[] , InterpretedFrame )
Exception : System.Management.Automation.ParameterBindingArgumentTransformationException
InvocationInfo : {New-AzSentinelAlertRule}
Line : New-AzSentinelAlertRule @AzureSentinelWorkSpaceInfo @AnalyticsRuleData

Position : At C:\Users\adminuser\Desktop\rules.ps1:769 char:61
+ ... ew-AzSentinelAlertRule @AzureSentinelWorkSpaceInfo @AnalyticsRuleData
+ ~~~~~~~~~~~~~~~~~~
HistoryId : 2

Message : Cannot convert the "System.Object[]" value of type "System.Object[]" to type
"Microsoft.Azure.PowerShell.Cmdlets.SecurityInsights.Models.Api20210901Preview.EntityMapping".
StackTrace : at System.Management.Automation.ArgumentTypeConverterAttribute.Transform(EngineIntrinsics
engineIntrinsics, Object inputData, Boolean bindingParameters, Boolean bindingScriptCmdlet)
at System.Management.Automation.ParameterBinderBase.BindParameter(CommandParameterInternal
parameter, CompiledCommandParameter parameterMetadata, ParameterBindingFlags flags)
Exception : System.Management.Automation.ArgumentTransformationMetadataException
InvocationInfo : {New-AzSentinelAlertRule}
Line : New-AzSentinelAlertRule @AzureSentinelWorkSpaceInfo @AnalyticsRuleData

Position : At C:\Users\adminuser\Desktop\rules.ps1:769 char:61
+ ... ew-AzSentinelAlertRule @AzureSentinelWorkSpaceInfo @AnalyticsRuleData
+ ~~~~~~~~~~~~~~~~~~
HistoryId : 2

Message : Cannot convert the "System.Object[]" value of type "System.Object[]" to type
"Microsoft.Azure.PowerShell.Cmdlets.SecurityInsights.Models.Api20210901Preview.EntityMapping".
StackTrace : at
System.Management.Automation.LanguagePrimitives.ConvertCheckingForCustomConverter.Convert(Object
valueToConvert, Type resultType, Boolean recursion, PSObject originalValueToConvert, IFormatProvider
formatProvider, TypeTable backupTable)
at System.Management.Automation.LanguagePrimitives.ConversionData`1.Invoke(Object valueToConvert,
Type resultType, Boolean recurse, PSObject originalValueToConvert, IFormatProvider formatProvider,
TypeTable backupTable)
at System.Management.Automation.LanguagePrimitives.ConvertTo(Object valueToConvert, Type
resultType, Boolean recursion, IFormatProvider formatProvider, TypeTable backupTypeTable)
at System.Management.Automation.ArgumentTypeConverterAttribute.Transform(EngineIntrinsics
engineIntrinsics, Object inputData, Boolean bindingParameters, Boolean bindingScriptCmdlet)
Exception : System.Management.Automation.PSInvalidCastException
InvocationInfo : {New-AzSentinelAlertRule}
Line : New-AzSentinelAlertRule @AzureSentinelWorkSpaceInfo @AnalyticsRuleData

Position : At C:\Users\adminuser\Desktop\rules.ps1:769 char:61
+ ... ew-AzSentinelAlertRule @AzureSentinelWorkSpaceInfo @AnalyticsRuleData
+ ~~~~~~~~~~~~~~~~~~
HistoryId : 2
```