Assign setup_for_company to namespace in reg flow

What does this MR do and why?

Assign setup_for_company to namespaces in the registration flow. This attribute is assigned to User records in the registration flow but we also want it on Namespace.

part of: #337360

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Register as a new user
2. On the registration welcome screen, select either "My company or team", or "just me" (this is the setup_for_company attribute)
3. Ensure after registration that the value for setup_for_company is identical and on the user record as well as the namespace record created in the registration flow.

MR acceptance checklist

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