Feat/add local volumes backup (#821)

* Add Backup Docker Volumes Locally

* Update naming

public/v4/apps/offen-local-docker-backup.yml

@@ -0,0 +1,51 @@
+captainVersion: 4
+services:
+    $$cap_appname:
+        image: offen/docker-volume-backup:$$cap_version
+        environment:
+            BACKUP_FILENAME: $$cap_backup_filename
+            BACKUP_ARCHIVE: /archive
+            BACKUP_CRON_EXPRESSION: $$cap_backup_cron_expression
+            BACKUP_RETENTION_DAYS: $$cap_backup_retention_days
+        volumes:
+            - $$cap_volume_to_backup:/backup/data
+            - $$cap_backup_path:/archive
+        restart: always
+        caproverExtra:
+            notExposeAsWebApp: 'true'
+caproverOneClickApp:
+    variables:
+        - id: $$cap_version
+          label: Docker volume backup version
+          defaultValue: 'v2'
+          description: Check out their Docker page for the valid tags https://hub.docker.com/r/offen/docker-volume-backup/tags
+          validRegex: /^([^\s^\/])+$/
+        - id: $$cap_volume_to_backup
+          label: Volume to backup
+          description: Path of the volume that you want to backup, e.g. `/var/lib/docker/volumes/captain--my-app/_data`
+        - id: $$cap_backup_path
+          label: Backup path
+          defaultValue: '/backups'
+          description: Path where you want to store the backups
+        - id: $$cap_backup_filename
+          label: Backup filename
+          defaultValue: 'backup-%Y-%m-%dT%H-%M-%S.tar.gz'
+          description: The name of the backup file including the `.tar.gz` extension. Format verbs will be replaced as in `strftime`. Omitting them will result in the same filename for every backup run, which means previous versions will be overwritten on subsequent runs. The default results in filenames like `backup-2021-08-29T04-00-00.tar.gz`.
+        - id: $$cap_backup_cron_expression
+          label: Cron expression
+          defaultValue: '@daily'
+          description: Backups run on the given cron schedule in `busybox` flavor. If no value is set, `@daily` will be used. If you do not want the cron to ever run, use `0 0 5 31 2 ?`.
+        - id: $$cap_backup_retention_days
+          label: Backup retention days
+          defaultValue: '14'
+          description: Define this value to enable automatic rotation of old backups. The value declares the number of days for which a backup is kept.
+    instructions:
+        start: >-
+            Backup Docker volumes locally. See https://github.com/offen/docker-volume-backup.
+        end: >-
+            Aaaand you're done! 😄
+            Your service is up and running
+    displayName: Docker volume backup
+    isOfficial: true
+    description: Backup Docker volumes locally
+    documentation: Taken from https://github.com/offen/docker-volume-backup