Add-AzSqlElasticJobStep missing parameter -MaxParallelism

## Description
Per this document (https://github.com/MicrosoftDocs/azure-docs/blob/master/articles/sql-database/elastic-jobs-overview.md) you are expected to pass `-MaxParallelism` to limit concurrency. This parameter does not exists for Add-AzSqlElasticJobStep module

## Steps to reproduce

```powershell
Add-AzSqlElasticJobStep -MaxParallelism
```

## Module versions

```powershell
PS C:\Users\174181> get-installedmodule az.sql

Version Name Repository Description
------- ---- ---------- -----------
1.14.0 Az.Sql PSGallery Microsoft Azure PowerShell - SQL service cmdlets for Azure Resource Manager in Windows PowerShell and PowerShell Core.…
```