Fix docs for the cells administration helm config example

What does this MR do and why?

Fixing the documentation for the Cells administration via Helm Chart.

Looking at the original MR and master branch, the topologyServiceClient and database need to be indented inside the cell block.

References

Original MR in Helm Charts, introducing these fields: gitlab-org/charts/gitlab!4111 (merged) Master branch on the Helm Charts: https://gitlab.com/gitlab-org/charts/gitlab/-/blob/master/charts/gitlab/templates/_gitlab.yaml.tpl?ref_type=heads

part of: gitlab-com/gl-infra/tenant-scale/cells-infrastructure/team#244 (closed)