Fix signing for .nupkg, defining ADO variable

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#### AI description  (iteration 1)
#### PR Classification
Bug fix to resolve issues with signing .nupkg packages in the pipeline.

#### PR Summary
This pull request adjusts the pipeline steps to ensure the correct directory path is used for signing the .nupkg, while adding debugging steps to verify the directory contents before and after signing.
- `/pipelines/PSResourceGet-Official.yml`: Introduces a `publishPath` variable using `Join-Path` to reliably point to the `PublishedNupkg` directory.
- `/pipelines/PSResourceGet-Official.yml`: Updates registration, signing, and directory navigation steps to use `publishPath` instead of hardcoded paths, and adds commands to output folder contents for debugging.
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…lishPath var reference

Remove isOutput on variable being set and update publishPath var reference

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#### AI description  (iteration 1)
#### PR Classification
This pull request is a pipeline fix and code cleanup, adjusting variable setting and reference for improved consistency.

#### PR Summary
The changes remove the "isOutput=true" flag when setting the "publishPath" variable and update the file copy step to correctly reference the "publishPath".
- `/.pipelines/PSResourceGet-Official.yml`: Removed the "isOutput=true" from the variable setting command.
- `/.pipelines/PSResourceGet-Official.yml`: Updated the file copy task to use `publishPath` instead of `signOutPath` for selecting the published package.
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Add ob_restore_phase to steps in packaging job