CONTRIBUTING: Simplify error handling guidelines - use Write-Error

[Copilot]

• Update AI instructions: clarify return only needed for non-terminating Write-Error
• Update CONTRIBUTING.md: clarify return usage and remove it from -ErrorAction Stop example
• Fix markdown table formatting: remove leading/trailing pipes to satisfy MD055
• All code review feedback addressed

Original prompt

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This section details on the original issue you should resolve

<issue_title>CONTRIBUTING: Update information around $PSCmdlet.ThrowTerminatingError</issue_title>
<issue_description>The documentation should be updated according to this: #1966 (comment)

Also reference: https://stackoverflow.com/questions/49204918/difference-between-throw-and-pscmdlet-throwterminatingerror

SqlServerDsc/CONTRIBUTING.md

Lines 368 to 379 in 3c30929

	When instead using `$PSCmdlet.ThrowTerminatingError()`:
	```powershell
	$PSCmdlet.ThrowTerminatingError(
	[System.Management.Automation.ErrorRecord]::new(
	'MyError',
	'GS0001',
	[System.Management.Automation.ErrorCategory]::InvalidOperation,
	'MyObjectOrValue'
	)
	)
	```

I caught this today where I call a public command (or function) from a another public command. Example below.

function Get-Something
{
    [CmdletBinding()]
    param ()

    $PSCmdlet.ThrowTerminatingError(
        [System.Management.Automation.ErrorRecord]::new(
            'Error message',
            'CODE',
            [System.Management.Automation.ErrorCategory]::InvalidOperation,
            'MyObject'
        )
    )

    "Get-Something exiting" # CORRECT: Does not hit this
}

function Start-Something
{
    [CmdletBinding()]
    param ()

    Get-Something -Name $null -ErrorAction 'Stop'

    "Started" # BUG: This line is executed even though Get-Something throw an exception
}

# This hits the bug in Start-Something
Start-Something

# The user must add -ErrorAction 'Stop' to Start-Something to avoid the bug which is not intuitive
Start-Something -ErrorAction 'Stop'

Similar but using Write-Error (non-terminating error):

function Get-Something
{
    [CmdletBinding()]
    param ()

    Write-Error -Message 'Error message' -Category InvalidOperation -TargetObject 'MyObject' -ErrorId 'CODE'

    "Get-Something exiting" # CORRECT: Does not hit this
}

function Start-Something
{
    [CmdletBinding()]
    param ()

    Get-Something -Name $null -ErrorAction 'Stop'

    "Started" # CORRECT: Does not hit this
}

# This works as expected, stops after the exception in Get-Something
Start-Something
```</issue_description>

<agent_instructions>Read the issue and comment, follow the links and read those comments and links. Based on that make a conclusion about how to best use different ways of throwing a terminating and non-terminating error in public commands and update CONTRIBUTING.md. We should never use `throw` in public commands though, so that is not in scope. My basic understanding is that we should use `Write-Error` whenever possible, but should we limit or entirely not use `$PSCmdlet.ThrowTerminatingError()`? What scenarios should we use each in, and if possible give examples of scenarios where each option fail and where they succeed. We have scenarios like commands accepting pipeline input (that process several items at a time over pipeline), not accepting pipeline input, commands that should never throw a terminating error by default but a non-terminating error and commands that in certain code paths must throw a terminating error.</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes CONTRIBUTING: Update information around $PSCmdlet.ThrowTerminatingError #2045

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This change is