Provide Details for moving from Cluster to single node Gitaly

We need a process where an existing customer can move from a Gitaly cluster back to a single node/a non-gitaly cluster. This should be a method to undo the Gitaly Cluster. We need this anyways as there could be business reasons a customer wants to move a repo off of Gitaly cluster. We should provide it in a way that allows customers some level of decision making (per repo efforts?). For first iteration it can be simpler though.

We want to provide clear documentation and steps how to do this.