Replace inconsistent backend-node term

The admin docs primary use the term "Gitaly node" to refer to
Gitaly servers proxied by Praefect. The term "Backend node" is
used to mean the same thing. This change further aligns the docs
with the term "Gitaly node".

doc/administration/gitaly/praefect.md

@@ -1172,7 +1172,7 @@ The source must be on a later version than the target storage.
 sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml reconcile -virtual <virtual-storage> -reference <up-to-date-storage> -target <outdated-storage> -f
 ```
 
-Refer to [Backend Node Recovery](#backend-node-recovery) section for more details on the `reconcile` sub-command.
+Refer to [Gitaly node recovery](#gitaly-node-recovery) section for more details on the `reconcile` sub-command.
 
 ### Enable writes or accept data loss
 
@@ -1199,14 +1199,15 @@ CAUTION: **Caution:**
 `accept-dataloss` causes permanent data loss by overwriting other versions of the repository. Data
 [recovery efforts](#recover-missing-data) must be performed before using it.
 
-## Backend Node Recovery
+## Gitaly node recovery
 
-When a Praefect backend node fails and is no longer able to
-replicate changes, the backend node will start to drift from the primary. If
-that node eventually recovers, it will need to be reconciled with the current
-primary. The primary node is considered the single source of truth for the
-state of a shard. The Praefect `reconcile` sub-command allows for the manual
-reconciliation between a backend node and the current primary.
+When a secondary Gitaly node fails and is no longer able to replicate changes, it starts
+to drift from the primary Gitaly node. If the failed Gitaly node eventually recovers,
+it needs to be reconciled with the primary Gitaly node. The primary Gitaly node is considered
+the single source of truth for the state of a shard.
+
+The Praefect `reconcile` sub-command allows for the manual reconciliation between a secondary
+Gitaly node and the current primary Gitaly node.
 
 Run the following command on the Praefect server after all placeholders
 (`<virtual-storage>` and `<target-storage>`) have been replaced:
@@ -1215,8 +1216,8 @@ Run the following command on the Praefect server after all placeholders
 sudo /opt/gitlab/embedded/bin/praefect -config /var/opt/gitlab/praefect/config.toml reconcile -virtual <virtual-storage> -target <target-storage>
 ```
 
-- Replace the placeholder `<virtual-storage>` with the virtual storage containing the backend node storage to be checked.
-- Replace the placeholder `<target-storage>` with the backend storage name.
+- Replace the placeholder `<virtual-storage>` with the virtual storage containing the Gitaly node storage to be checked.
+- Replace the placeholder `<target-storage>` with the Gitaly storage name.
 
 The command will return a list of repositories that were found to be
 inconsistent against the current primary. Each of these inconsistencies will