feat: add migrate database from a source to a target databse

docs/how-tos/migrate.md

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+---
+title: Migrate database
+layout: default
+parent: How Tos
+nav_order: 9
+---
+
+# Migrate database
+
+To migrate the database, you need to add `migrate` command.
+
+{: .note }
+The pg backup has another great feature: migrating your database from a source database to another.
+
+As you know, to restore a database from a source to a target database, you need 2 operations: to start by backing up the source database and then restoring the source backed database to the target database.
+Instead of proceeding like that, you can use the integrated feature `(migrate)` that will help you to migrate your database by doing only one operation.
+
+
+### Docker compose
+```yml
+services:
+  pg-bkup:
+    # In production, it is advised to lock your image tag to a proper
+    # release version instead of using `latest`.
+    # Check https://github.com/jkaninda/pg-bkup/releases
+    # for a list of available releases.
+    image: jkaninda/pg-bkup
+    container_name: pg-bkup
+    command: migrate
+    volumes:
+      - ./backup:/backup
+    environment:
+      ## Target database
+      - DB_PORT=5432
+      - DB_HOST=postgres
+      - DB_NAME=database
+      - DB_USERNAME=username
+      - DB_PASSWORD=password
+      ## Source database
+      - SOURCE_DB_HOST=postgres
+      - SOURCE_DB_PORT=5432
+      - SOURCE_DB_NAME=sourcedb
+      - SOURCE_DB_USERNAME=jonas
+      - SOURCE_DB_PASSWORD=password
+    # pg-bkup container must be connected to the same network with your database
+    networks:
+      - web
+networks:
+  web:
+```
+
+### Migrate database using Docker CLI
+
+```env
+## Target database
+DB_PORT=5432
+DB_HOST=postgres
+DB_NAME=targetdb
+DB_USERNAME=targetuser
+DB_PASSWORD=password
+
+## Source database
+SOURCE_DB_HOST=postgres
+SOURCE_DB_PORT=5432
+SOURCE_DB_NAME=sourcedb
+SOURCE_DB_USERNAME=sourceuser
+SOURCE_DB_PASSWORD=password
+```
+
+```shell
+ docker run --rm --network your_network_name \
+ --env-file your-env
+ -v $PWD/backup:/backup/ \
+ jkaninda/pg-bkup migrate -d database_name
+```