[Eng]: AzPreview is not updated when a single module's version is bumped (OOB release)

[BethanyZhou]

Description

Before bumping: Az.Compute is 4.18.0
In 2 OOB releases: Az.Compute is 4.20.0
After merge code into main branch: Az.Compute is 4.20.0, Az.Compute is AzPreview.psd1 4.18.0

If we run azure-powershell-sign pipeline in this scenario, publish task fails as Az.Compute 4.18.0 doesn't exist, please refer to: https://dev.azure.com/azure-sdk/internal/_build/results?buildId=1212233&view=results

I would like to recommend 1 solution for this case:
Move the logic of generating AzPreview.psd1 into publish task so that we always are able to best-matched AzPreview.psd1 for current build.

[dingmeng-xue]

When the version of service module is not existing in Az.psd1, signing pipeline will download that version from PSGallery. Can AzPreview use the same logic?

As the result, AzPreview.psd1 is a snapshot of the latest released version. It is only updated when we release new Az.

[BethanyZhou]

Close as fixed.