Support reading timezone info from env (#748)

* add tzdata package

* updated timezone documentation

* add missing bind-mount from updated docs

* Add timezone deprecation warnings and related logging to backup commands

* fix lint CI job error

* Address PR comments: refactor timezone deprecation warning handling, update docs

docs/how-tos/set-container-timezone.md

@@ -1,26 +1,55 @@
 ---
-title: Set the timezone the container runs in
+title: Setting the Time Zone
 layout: default
 parent: How Tos
 nav_order: 8
 ---
 
-# Set the timezone the container runs in
+# Setting the Time Zone
 
-By default a container based on this image will run in the UTC timezone.
-As the image is designed to be as small as possible, additional timezone data is not included.
-In case you want to run your cron rules in your local timezone (respecting DST and similar), you can mount your Docker host's `/etc/timezone`, `/etc/localtime`, and `/usr/share/zoneinfo` in read-only mode:
+## Use Environment Variable `TZ`
+
+A container started using this image will default to UTC. To modify the time zone, set the `TZ` environment variable to a valid [tz database time zone](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones):
 
 ```yml
 services:
   backup:
-    image: offen/docker-volume-backup:v2
+    image: offen/docker-volume-backup:latest
+    environment:
+      - TZ=Europe/Berlin
     volumes:
       - data:/backup/my-app-backup:ro
-      - /etc/timezone:/etc/timezone:ro
-      - /etc/localtime:/etc/localtime:ro
-      - /usr/share/zoneinfo:/usr/share/zoneinfo:ro
 
 volumes:
   data:
 ```
+
+## Notes
+
+This approach is preferred because it:
+
+- avoids dependency on host configuration  
+- works consistently across environments  
+
+### Compatibility
+
+- Bind-mounting timezone files will continue to work if `TZ` is not set.
+- If `TZ` is set, it takes precedence over any bind-mounted timezone configuration.
+- An invalid `TZ` value will cause the container to default to UTC.
+
+:warning: **Deprecation Warning**  
+The method described below (bind-mounting files from the host) is **deprecated**. Please use the new method described above (`TZ`)
+
+> ```yml
+> services:
+>   backup:
+>     image: offen/docker-volume-backup:latest
+>     volumes:
+>       - data:/backup/my-app-backup:ro
+>       - /etc/timezone:/etc/timezone:ro
+>       - /etc/localtime:/etc/localtime:ro
+>       - /usr/share/zoneinfo:/usr/share/zoneinfo:ro
+>
+> volumes:
+>   data:
+> ```