Add backup_include / backup_exclude for partial backups (mariadb-backup --tables/--databases parity)

BACKUP SERVER currently backs up the whole instance. there is no way to back up a subset of databases (or) tables.
The legacy mariadb-backup tool supports this via --databases, --databases-exclude, --databases-file, --tables,
--tables-exclude, --tables-file. To make BACKUP SERVER a full replacement, add server-side include/exclude filtering.

Add two filter inputs, backup_include and backup_exclude, matching on fully-qualified db.table:

• backup_include — if set, copy only matching objects; unset = full backup (current behavior).
• backup_exclude — applied after include; exclude wins.
• Multiple includes union; multiple excludes union.
• InnoDB system tablespace, undo, redo log and the data dictionary are always included.
• A db.table filter selects all of that table's partitions

Mapping from the legacy CLI:

-databases/-databases-file should map to backup_include
--databases-exclude map to backup_exclude
--tables map to --backup_include (pass same POSIX)
--tables-exclude map to --backup_exclude (pass same REGEX)
--tables-file should map to backup_include (map each line of db.table)