Add organization_users entry on member invite acceptance

What does this MR do and why?

Add organization_users entry on member invite acceptance

• keep organization_users up to date for new organizations
• see #419366 (closed)

note https://gitlab.com/gitlab-org/gitlab/-/pipelines/1132819325 was ran with pipeline:run-all-rspec applied to ensure full coverage for query limits

MR acceptance checklist

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Related to #419366 (closed)