Get-AzRoleAssignmentScheduleInstance needs to support -Filter on all parametersets

### Description

It is currently not possible to use `Get-AzRoleAssignmentScheduleInstance` to fetch an individual instance without a privilege error for an unprivileged user unless `filter=asTarget()` is also specified, but there is no combination of parameter sets that allow this, `-Filter` is only allowed with a "naked" call and the scope parameter.

## Workaround
```ps
invoke-azrestmethod 'https://management.azure.com///providers/Microsoft.Authorization/roleAssignmentScheduleInstances/257498e2-xxxx-xxxx-xxxx-daaaee9025b3?$filter=asTarget%28%29&api-version=2020-10-01'`
```

### Issue script & Debug output

```PowerShell
N/A
```

### Environment data

```PowerShell
Name Value
---- -----
PSVersion 7.2.3
PSEdition Core
GitCommitId 7.2.3
OS Microsoft Windows 10.0.22610
Platform Win32NT
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1
WSManStackVersion 3.0
```

### Module versions

```PowerShell
ModuleType Version PreRelease Name ExportedCommands
---------- ------- ---------- ---- ----------------
Script 2.7.6 Az.Accounts {Add-AzEnvironment, Clear-AzContext, Clear-AzDefault, Connect-AzAccount…}
Script 5.6.0 Az.Resources {Export-AzResourceGroup, Export-AzTemplateSpec, Get-AzDenyAssignment, Get-AzDeployment…}
```

### Error output

_No response_

Start at the Get-AzRoleAssignmentScheduleInstance cmdlet and inspect how its parameter sets expose -Filter, then compare that behavior with the roleAssignmentScheduleInstances REST endpoint and its filter=asTarget() workaround. Done means the cmdlet accepts -Filter with the individual-instance parameter combinations and avoids the reported privilege error; add or update the relevant tests if the repository identifies them.

Written by the indexing model from the issue text.