Namespace api find un-replicated namespace from primary DB

What does this MR do and why?

For issue https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/9808+

Gitlab.com trial has a create group flow. In this flow, the Customer create a new group, and passing the group.id to CustomersDot API to create the trial. CustomersDot API will find the namespace data by calling GitLab namespace API, using the group ID. Sometimes the Gitlab database has a delay to replicate from primary DB to replicate DB. In this case, when CustomersDot find the namespace data using Gitlab namespace API, there is a chance the newly created group is not found in replication DB in Gitlab. This causes 404 not found error.

This MR stick the namespace ID when the new group is created in the create group trial flow. Then in Gitlab namespace API, it query the namespace from up-to-date replica DB(or primary DB). This ensures the newly created group be found correctly.

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Before	After
Trial with create group fail, due to namespace not found	Trial with create group succeed.

How to set up and validate locally

1. Enable database load balancing feature in GDK, following this documentation. Especially make sure to Simulating replication delay
2. Start Gitlab application and CustomersDot application
3. In Gitlab application, create a new group, go to group billing page

My local test result

4. On group billing page, click the button Start free trial of GitLab Ultimate and GitLab Duo Enterprise, fill in required data, and click Continue button

My local test result

5. Select create group, and click Activate my trial. It should succeed.

My local test result

6. Switch to master branch, repeat the same test in step 3/4/5, the trial creation failed due to namespace not found.

My local test result