Provide some warning / error in case of `gitlab-secrets.json` mismatch on Geo nodes
Description
Geo documentation states:
GitLab stores a number of secret values in the /etc/gitlab/gitlab-secrets.json file which must match between the primary and secondary nodes. Until there is a means of automatically replicating these between nodes (see issue gitlab-org/gitlab-ee#3789), they must be manually replicated to the secondary.
Proposal
In case of the keys mismatch, it would be nice to have some warning / error that prevents writing the data.