feat: add backup all databases

docs/how-tos/backup-all.md

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+---
+title: Backup all databases in the server
+layout: default
+parent: How Tos
+nav_order: 12
+---
+
+# Backup All Databases
+
+MySQL-Bkup supports backing up all databases on the server using the `--all-databases` (`-a`) flag. By default, this creates separate backup files for each database. If you prefer a single backup file, you can use the `--all-in-on`e (`-A`) flag.
+
+Backing up all databases is useful for creating a snapshot of the entire database server, whether for disaster recovery or migration purposes.
+## Backup Modes
+
+### Separate Backup Files (Default)
+
+Using --all-databases without --all-in-one creates individual backup files for each database.
+
+- Creates separate backup files for each database.
+- Provides more flexibility in restoring individual databases or tables.
+- Can be more manageable in cases where different databases have different retention policies.
+- Might take slightly longer due to multiple file operations.
+- It is the default behavior when using the `--all-databases` flag.
+- It does not backup system databases (`information_schema`, `performance_schema`, `mysql`, `sys`, `innodb`).
+
+**Command:**
+
+```bash
+docker run --rm --network your_network_name \
+  -v $PWD/backup:/backup/ \
+  -e "DB_HOST=dbhost" \
+  -e "DB_PORT=3306" \
+  -e "DB_USERNAME=username" \
+  -e "DB_PASSWORD=password" \
+  jkaninda/mysql-bkup backup --all-databases
+```
+### Single Backup File
+
+Using --all-in-one (-A) creates a single backup file containing all databases.
+
+- Creates a single backup file containing all databases.
+- Easier to manage if you need to restore everything at once.
+- Faster to back up and restore in bulk.
+- Can be problematic if you only need to restore a specific database or table.
+- It is recommended to use this option for disaster recovery purposes.
+- It backups system databases as well.
+
+```bash
+docker run --rm --network your_network_name \
+  -v $PWD/backup:/backup/ \
+  -e "DB_HOST=dbhost" \
+  -e "DB_PORT=3306" \
+  -e "DB_USERNAME=username" \
+  -e "DB_PASSWORD=password" \
+  jkaninda/mysql-bkup backup --all-in-one
+```
+
+### When to Use Which?
+
+- Use `--all-in-one` if you want a quick, simple backup for disaster recovery where you'll restore everything at once.
+- Use `--all-databases` if you need granularity in restoring specific databases or tables without affecting others.