Add an offline backup/restore engine in `tools.backup`:
- format based on XEP-0227 (pie), extended with Libervia sections
- handle several data types (params, private, roster, pep , gpg, files and db)
- per profile export/import and global handlers
- a manifest is used to have metadata and checksums
- full database snapshot/restore with the `db` type
- sqla: add `get_db_url`
- tools.common.utils: add `is_safe_relpath` and `is_process_running`
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