ci: also publish preview with "test" documentation content

[tbouffard]

This lets covers more use cases, in particular

• components with several versions, including alpha, beta and other pre-releases (validates the custom antora extension)
• custom messages
• verification of xref

Also introduce a new option in the preview script to change the Antora log level and use it when building the "test content" preview.

[github-actions[bot]]

:recycle: PR Preview 96f0e96f4e0611ccc27812e337ebe25270777ecf has been successfully destroyed since this PR has been closed.

_{🤖 By surge-preview}

[github-actions[bot]]

:recycle: PR Preview 96f0e96f4e0611ccc27812e337ebe25270777ecf has been successfully destroyed since this PR has been closed.

_{🤖 By surge-preview}

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

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0.0% Duplication

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