v2.6.30

IMPROVEMENTS

• add in REST API operation_id to result for all asynchronous commands (create,upload,download,restore) which allow poll /backup/status more precise, fix 1189, thanks @lepetitops
• add POST /backup/create_remote and POST /backup/restore_remote to API
• add --hardlink-exists-files to download and restore_remote, works only with backups created with 2.6.30 plus clickhouse-backup version, fix 1164
• add hardlink_exists_files to API for POST /backup/download and POST /backup/restore_remote, works only with backups created with 2.6.30 plus clickhouse-backup version, fix 1164