Onboarding project welcome viewing to be based on policy

What does this MR do?

We make the onboarding project welcome views, based on owner policy rather than custom creator_id logic.

Opened a discussion with product how after the experiment concludes we may settle for a specific policy for several onboarding projects.

Related to #327874 (closed)

Does this MR meet the acceptance criteria?

Conformity

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  • [-] I have included a changelog entry.
  • I have not included a changelog entry because it's an experiment behind a feature flag_.
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Availability and Testing

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• [-] Tested in all supported browsers
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Security

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