Fix Invoke-PnPSiteTemplate parameter set to allow -Path with -InputInstance

[Copilot]

Fixes a parameter set resolution error that prevented using -Path and -InputInstance parameters together in Invoke-PnPSiteTemplate, despite this being documented as supported behavior in Example 9.

Problem

The cmdlet would throw this error when using both parameters:

Invoke-PnPSiteTemplate -Path .\ -InputInstance $template
# Error: Parameter set cannot be resolved using the specified named parameters.

This occurred because the -Path parameter was only defined for the "Path" parameter set, making it mutually exclusive with -InputInstance (which belongs to the "Instance" parameter set).

Solution

Added a second [Parameter] attribute to allow -Path in the "Instance" parameter set as an optional parameter:

[Parameter(Mandatory = true, Position = 0, ValueFromPipelineByPropertyName = true, ValueFromPipeline = true, ParameterSetName = "Path")]
[Parameter(Mandatory = false, ParameterSetName = "Instance")]
public string Path;

This change:

• ✅ Preserves existing behavior: -Path remains mandatory in "Path" parameter set
• ✅ Enables documented behavior: -Path is now optional in "Instance" parameter set for specifying supporting file locations
• ✅ No breaking changes: All existing parameter combinations continue to work
• ✅ Implementation ready: The execution logic already supports this scenario (lines 279-294)

Usage

Now works as documented in Example 9:

# Get template instance in memory
$template = Get-PnPSiteTemplate -OutputInstance

# Apply with supporting files from specific path
Invoke-PnPSiteTemplate -InputInstance $template -Path .\supporting-files\

Fixes #4986.

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