Add configurable retries for locked SQLite backups

Add SQLITE_TIMEOUT, BACKUP_RETRIES, and BACKUP_RETRY_DELAY
environment variables to handle "database is locked" errors during
backup. Retry the sqlite3 .backup command with configurable timeouts
and delays, and clean up any WAL/SHM files that may interfere with
subsequent attempts. Bump version to 1.2.2.

.env.example

@@ -3,6 +3,9 @@ CRONTAB="00 06 * * *"
 DELETE_AFTER=10
 KEEP_LAST=10
 TZ=Asia/Novosibirsk
+SQLITE_TIMEOUT=60000
+BACKUP_RETRIES=5
+BACKUP_RETRY_DELAY=30
 MINIO_PATH=myminio://sqlite/master/
 MINIO_ACCOUNT_ID=account
 MINIO_APPLICATION_KEY=key