Fix pipeline 1009351 due to default_value_for

What does this MR do and why?

Replace default_value_for with Rails attributes API on issue tracker in JH.

Part one

Changes from:

• Upstream Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/378997
• Upstream MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/112164/diffs

NoMethodError: undefined method `default_value_for' for Integrations::Ones:Class

default_value_for is a method from the removed Gem.

The current version of default_value_for does not support Rails 7 and it looks almost unmaintained

In Rails 6 we can use the attributes API to set default values

Part two

Changes from:

• Upstream Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/388970
• Upstream MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/111324

Failure/Error: expect(page).to have_content('Creating your onboarding experience...')

Learn GitLab should no longer be created as its own project

How to set up and validate locally

gdk start

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