Register-AzMigrateProjectTool cmdlet not working

## Description

Running `Register-AzMigrateProjectTool` is not working and doesn't register any migration tools. `-Tool` parameter is not well documented (missing what values it can have) and it doesn't restrict to any tool that the migrate supports.

How can you register Azure Migrate tool to Azure Migrate project? That should the most common use case and it is not documented what the -Tool parameter should be.

Would expect to able to tab cycle different tool options for the -Tool param. It should not be a free string parameter where you can input any string.

## Steps to reproduce

```powershell
Register-AzMigrateProjectTool -MigrateProjectName migr-test -ResourceGroupName rg-migrate -Tool "Azure Migrate"
```

## Environment data

Local laptop powershell environment, Windows 10

```
Name Value
---- -----
PSVersion 7.1.1
PSEdition Core
GitCommitId 7.1.1
OS Microsoft Windows 10.0.19042
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
Script 1.0.1 Az.Migrate
```

## Debug output

```
VERBOSE: Performing the operation "Register-AzMigrateProjectTool_RegisterExpanded" on target "Call remote 'MigrateProjectsRegisterTool' operation".
True
```

Start by reproducing the documented command with Register-AzMigrateProjectTool and the shown -Tool value in the Az.Migrate module. Read the cmdlet's parameter behavior and the Azure Migrate tool-registration operation, then verify which supported tool values are accepted and that registration succeeds. Done means valid tools are discoverable or constrained and the common Azure Migrate registration path works as documented.

Written by the indexing model from the issue text.