[Doc]: New-AzSqlDatabaseExport Doesn't Contain Guidance for Managed Identity

### Type of issue

Missing information

### Feedback

Hello,

I have been trying to use the updated New-AzSqlDatabaseExport cmdlet with Managed Identity, but I keep running into:
` | Cannot process command because of one or more missing mandatory
| parameters: AdministratorLogin AdministratorLoginPassword.
`

What should these fields be for utilizing ManagedIdentity for the Database Export capability?

Looks like this is the PR that introduced the verbiage about managed identity: https://github.com/Azure/azure-powershell/pull/26884

Thank you

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