Update free user cap docs for public and personal namespaces

What does this MR do and why?

updates the docs to reflect change in direction via https://gitlab.com/gitlab-org/gitlab/-/issues/370616

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #363493