docs: update backup-and-restore.md (#21065)

* Update backup-and-restore.md

Added, and consolidated messaging across the md file in relation to updating the username when running scripts.

* chore: formatting

---------

Co-authored-by: Jason Rasmussen <jason@rasm.me>

docs/docs/administration/backup-and-restore.md

@@ -57,6 +57,7 @@ Then please follow the steps in the following section for restoring the database
   <TabItem value="Linux system" label="Linux system" default>
 
 ```bash title='Backup'
+# Replace <DB_USERNAME> with the database username - usually postgres unless you have changed it.
 docker exec -t immich_postgres pg_dumpall --clean --if-exists --username=<DB_USERNAME> | gzip > "/path/to/backup/dump.sql.gz"
 ```
 
@@ -69,6 +70,7 @@ docker compose create           # Create Docker containers for Immich apps witho
 docker start immich_postgres    # Start Postgres server
 sleep 10                        # Wait for Postgres server to start up
 # Check the database user if you deviated from the default
+# Replace <DB_USERNAME> with the database username - usually postgres unless you have changed it.
 gunzip --stdout "/path/to/backup/dump.sql.gz" \
 | sed "s/SELECT pg_catalog.set_config('search_path', '', false);/SELECT pg_catalog.set_config('search_path', 'public, pg_catalog', true);/g" \
 | docker exec -i immich_postgres psql --dbname=postgres --username=<DB_USERNAME>  # Restore Backup
@@ -79,6 +81,7 @@ docker compose up -d            # Start remainder of Immich apps
   <TabItem value="Windows system (PowerShell)" label="Windows system (PowerShell)">
 
 ```powershell title='Backup'
+# Replace <DB_USERNAME> with the database username - usually postgres unless you have changed it.
 [System.IO.File]::WriteAllLines("C:\absolute\path\to\backup\dump.sql", (docker exec -t immich_postgres pg_dumpall --clean --if-exists --username=<DB_USERNAME>))
 ```
 
@@ -92,7 +95,9 @@ docker compose create                             # Create Docker containers for
 docker start immich_postgres                      # Start Postgres server
 sleep 10                                          # Wait for Postgres server to start up
 docker exec -it immich_postgres bash              # Enter the Docker shell and run the following command
-# Check the database user if you deviated from the default. If your backup ends in `.gz`, replace `cat` with `gunzip --stdout`
+# If your backup ends in `.gz`, replace `cat` with `gunzip --stdout`
+# Replace <DB_USERNAME> with the database username - usually postgres unless you have changed it.
+
 cat "/dump.sql" | sed "s/SELECT pg_catalog.set_config('search_path', '', false);/SELECT pg_catalog.set_config('search_path', 'public, pg_catalog', true);/g" | psql --dbname=postgres --username=<DB_USERNAME>
 exit                                              # Exit the Docker shell
 docker compose up -d                              # Start remainder of Immich apps