Move rest of content from GitLab docs to Gitaly example config file
requested to merge eread/move-rest-of-content-from-gitlab-docs-to-gitaly-example-configuration-file into master
Following on from: !6568 (merged), copy more of the content from https://docs.gitlab.com/ee/administration/gitaly/reference.html, to make sure nothing is lost so that we can eventually point readers to these configuration files as the source of truth.
Eventually, we might publish the configuration file content back to GitLab docs: #4651.