Pass user id to CustomersDot fetch payment form

What does this MR do and why?

Pass user id in payment_forms call to CustomersDot. This will be further used in CustomersDot to decide which Zuora HPM to return since we want to implement a User Id based feature flag strategy to enable the new Zuora 3DS enabled HPM only for certain internal Gitlab users initially.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

No UX changes.

How to set up and validate locally

1. Login to your GDK and check your user id (Go to profile page - http://localhost:3000/-/user_settings/profile and then see User Id field value - screenshot below)
2. Ensure that CustomersDot is running.
3. Add a print (pp(params[:user_id])) or debugger here in CustomersDot codebase.
4. Go to http://localhost:3000/-/subscriptions/new?plan_id=2c92a00d76f0d5060176f2fb0a5029ff&test=capabilities
5. Check in CustomersDot logs or debugger that the user_id is passed correctly.

Related to https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/9246