Cell ID to default to null instead of 1

What does this MR do and why?

Cell ID to default to null instead of 1

Addressing:

• #510193 (closed)
• Additionally it's also addressing #506660 (closed) because it's relevant.

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.

How to set up and validate locally

• Restart GDK and make sure you can use GitLab as usual

• Exclude the primary Cell from the Cells Cluster, and use it as normal https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/cells.md?ref_type=heads#excluding-the-primary-cell-cell-1-from-the-cluster

Related to #510193 (closed)