Update Gitaly Server docs to use `git_data_dirs`

4 jobs for !18640 with wc-use-git_data_dirs in 3 minutes and 27 seconds
detached
Status Job ID Name Coverage
  Test
passed #322136561
gitlab-org
danger-review

00:02:49

passed #322136560
gitlab-org
docs lint

00:03:27

 
  Review
manual #322136563
gitlab-org allowed to fail manual
review-docs-cleanup
manual #322136562
gitlab-org allowed to fail manual
review-docs-deploy