(dsc): `PSResourceList` manifest migration for deprecated `whatIf` to `set.whatIfArg`

Locate psresourcelist.dsc.resource.json, the Repository manifest, and the README. Compare the existing set and what-if commands with the DSC 3.2.0 whatIfArg schema, then validate the -File invocation with stdin input in pwsh. Done means both manifests use the supported schema and exit handling, and the README states the minimum DSC version.

Summary of the new feature / enhancement

psresourcelist.dsc.resource.json implements what-if through the top-level whatIf manifest operation. DSC deprecated that operation in 3.2.0 in favour of set.whatIfArg, where the engine appends an argument to the normal set command instead of running a separate command. Staying on whatIf means a deprecation warning today and a break when the property is removed.

Current manifest:

"whatIf": {
  "executable": "pwsh",
  "args": [ "-NoLogo", "-NonInteractive", "-NoProfile", "-ExecutionPolicy", "Bypass", "-Command",
            "$Input | ./psresourceget.ps1 -resourcetype 'psresourcelist' -operation set -WhatIf; exit $LASTEXITCODE" ],
  "input": "stdin",
  "return": "state"
}

Proposed technical implementation details (optional)

• Replace the whatIf block with "whatIfArg": "-WhatIf" inside set.
• whatIfArg is appended after the existing args, which does not work with -Command "...". Switch set to -File ./psresourceget.ps1 -ResourceType psresourcelist -Operation set so the appended -WhatIf binds to the script's [switch]$WhatIf. Verified locally that pwsh -File with stdin input works for this script.
• Bump $schema on both manifests to a version that includes whatIfArg and set the minimum supported DSC version to 3.2.0 in the README.
• While in the manifests, the Repository manifest's -Command invocations should also gain ; exit $LASTEXITCODE or move to -File