Refresh service_account_token for kubernetes_namespaces

This is safer considering some project level clusters may see a change in behaviour if we merge this first. Update: does not actually change behaviour for project-level clusters, so we should be safe to merge this by itself.

What does this MR do?

There seems to be several examples where service_account_token is blank even in GitLab.com newly created kubernetes_namespaces . We have not figured out why they are blank but this should hopefully fix some issues similar to https://gitlab.com/gitlab-org/gitlab-ce/issues/55362

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

#55362 (closed)