Handle Praefect db migrations correctly

Closes https://gitlab.com/gitlab-org/quality/gitlab-environment-toolkit/-/issues/104

Relates gitaly#3557 (closed)

MR adds handling for Praefect auto migration requirements where only one node (deploy node) should be running the migrations first before the rest of the nodes are upgraded - not unlike GitLab Rails.

Introduces a slightly new approach to both Praefect and GitLab Rails migrations where we now just rely on Ansible's run_once flag instead of always running on the tagged Primary nodes. This reduces the reliance on the primary tagging from Terraform, something we may want to continue to reduce in the future as more complex setups come in.