Initialize-AzMigrateReplicationInfrastructure needs the ability to accept UserObjectId as a parameter.

## User Object ID Parameter for Initialize-AzMigrateReplicationInfrastructure

When calling Initialize-AzMigrateReplicationInfrastructure I need the ability to pass the User Object ID as a parameter for situations where the existing code will not be able to resolve the User Object ID. Examples of when I need this are running Initialize-AzMigrateReplicationInfrastructure using a service principal or an account that is external to the tenant.

## Proposed implementation details (optional)

Add a parameter to the Initialize-AzMigrateReplicationInfrastructure cmdlet called `UserId ` that allows a User Object ID to be specified for the cmdlet to use.

Start by locating the Initialize-AzMigrateReplicationInfrastructure cmdlet implementation and reviewing how its existing parameters are defined and used. Verify the cmdlet can accept a UserId value for service-principal or external-tenant scenarios, and confirm the existing behavior remains intact when the parameter is not supplied.

Written by the indexing model from the issue text.