(Central Management) Add API documentation example for advanced deployment steps

Originally from https://github.com/chocolatey/chocolatey-licensed-issues/issues/291

> Currently using the /api/services/app/DeploymentPlans/CreateOrEdit API call. You are only able to specify a basic deployment step of installing, upgrading, or uninstalling a specific package.
>
> Would like the capability to enter in Powershell to run an advanced deployment instead of just being tied to the options of a basic deployment step. Such as stopping services and other powershell operations.

(...)

> This feature already exists, though we could definitely use better documentation around it. The essence of it is that it's very similar to a basic step, but you need to target a slightly different API endpoint, and the script property is then interpreted as a full PowerShell script.
>
> Taking the example from our [api examples](https://docs.chocolatey.org/en-us/central-management/usage/api/examples#add-a-deployment-step) for a basic step, it can be modified so the step is considered an Advanced step:

```powershell
$params = @{
# Note the `CreateOrEditPrivileged` endpoint is used for advanced steps instead of `CreateOrEdit`
Uri = "https://$CcmServerHostname/api/services/app/DeploymentSteps/CreateOrEditPrivileged"
Method = "POST"
WebSession = $Session
ContentType = 'application/json'
Body = @{
deploymentPlanId = $deployment.Id
name = "Choco Upgrade All"
validExitCodes = "0, 1605, 1614, 1641, 3010"
executionTimeoutInSeconds = 14400
machineContactTimeoutInMinutes = "0"
failOnError = $true
requireSuccessOnAllComputers = $false
deploymentStepGroups = @(
@{ groupId = $Group.Id; groupName = $Group.Name }
)
# For advanced steps, enter a powershell script as a string
script = 'Write-Host "This is treated as a PowerShell script"'
} | ConvertTo-Json
}
$null = Invoke-RestMethod @params
```

> Note that this won't work if the user you're working with the API from doesn't have permissions to use Advanced steps in deployments.