Add configuration for locating gitaly-backup

`gitaly.client_path` has been removed. So we need a specific
configuration for finding gitaly-backup. CNG will likely install the
binary on the container path. So it's useful to search path as a
fallback.

Changelog: added

config/gitlab.yml.example

@@ -1116,6 +1116,7 @@ production: &base
   ## Backup settings
   backup:
     path: "tmp/backups"   # Relative paths are relative to Rails.root (default: tmp/backups/)
+    # gitaly_backup_path: # Path of the gitaly-backup binary (default: searches $PATH)
     # archive_permissions: 0640 # Permissions for the resulting backup.tar file (default: 0600)
     # keep_time: 604800   # default: 0 (forever) (in seconds)
     # pg_schema: public     # default: nil, it means that all schemas will be backed up
@@ -1431,6 +1432,7 @@ test:
     secret_file: tmp/gitlab_workhorse_test_secret
   backup:
     path: tmp/tests/backups
+    gitaly_backup_path: tmp/tests/gitaly/_build/bin/gitaly-backup
   pseudonymizer:
     manifest: config/pseudonymizer.yml
     upload:

config/initializers/1_settings.rb

@@ -793,6 +793,7 @@ Settings.backup['upload']['multipart_chunk_size'] ||= 104857600
 Settings.backup['upload']['encryption'] ||= nil
 Settings.backup['upload']['encryption_key'] ||= ENV['GITLAB_BACKUP_ENCRYPTION_KEY']
 Settings.backup['upload']['storage_class'] ||= nil
+Settings.backup['gitaly_backup_path'] ||= Gitlab::Utils.which('gitaly-backup')
 
 #
 # Pseudonymizer

lib/backup/gitaly_backup.rb

@@ -61,7 +61,7 @@ module Backup
     end
 
     def bin_path
-      File.absolute_path(File.join(Gitlab.config.gitaly.client_path, 'gitaly-backup'))
+      File.absolute_path(Gitlab.config.backup.gitaly_backup_path)
     end
   end
 end