feat: add encrypt backup using public key, migrate gpg to go gpg dependency

docs/how-tos/encrypt-backup.md

@@ -10,15 +10,17 @@ The image supports encrypting backups using one of two available methods: GPG wi
 
 ## Using GPG passphrase
 
-The image supports encrypting backups using GPG out of the box. In case a `GPG_PASSPHRASE` environment variable is set, the backup archive will be encrypted using the given key and saved as a sql.gpg file instead or sql.gz.gpg.
+The image supports encrypting backups using GPG out of the box. In case a `GPG_PASSPHRASE` or `GPG_PUBLIC_KEY` environment variable is set, the backup archive will be encrypted using the given key and saved as a sql.gpg file instead or sql.gz.gpg.
 
 {: .warning }
 To restore an encrypted backup, you need to provide the same GPG passphrase used during backup process.
-Or 
 
 - GPG home directory `/config/gnupg`
 - Cipher algorithm `aes256`
 
+{: .note }
+The backup encrypted using `GPG passphrase` method can be restored automatically, no need to decrypt it before restoration.  
+
 
 To decrypt manually, you need to install `gnupg`
 
@@ -27,7 +29,10 @@ gpg --batch --passphrase "my-passphrase" \
 --output database_20240730_044201.sql.gz \
 --decrypt database_20240730_044201.sql.gz.gpg
 ```
-
+Using your private key
+```shell
+gpg --output database_20240730_044201.sql.gz --decrypt database_20240730_044201.sql.gz.gpg
+```
 ### Backup
 
 ```yml
@@ -56,4 +61,3 @@ services:
 networks:
   web:
 ```
-## Using GPG public key