Clone: Support Local Clone

Specification:
1. Install clone plugin to use the feature.

INSTALL PLUGIN clone SONAME 'mariadb_clone';

SHOW PLUGINS;

SELECT * FROM information_schema.plugins where plugin_name like "%clone%" \G

2. New BACKUP_ADMIN privilege to allow user to take a snapshot of the entire data directory.

CREATE USER clone IDENTIFIED by 'clone_pass';

GRANT BACKUP_ADMIN ON *.* to clone;

3. Clone command to clone Innodb and ARIA tables including system tables.

CLONE LOCAL DATA DIRECTORY [=]  '<absolute path to target directory';

• Have ARIA and Innodb tables and concurrent DML operations during clone.

4. Start server on cloned data directory and check all tables are cloned.

5. Uninstall clone plugin.

UNINSTALL PLUGIN clone;

Limitations
1. Not supported for Innodb encrypted table [would return error] : Implemented by MDEV-36745
2. Not supported for Innodb page compressed table [would return error] : Implemented by MDEV-36746
3. Any tables in SE other than Innodb or ARIA are not cloned : Implemented in MDEV-36739
4. Binary Log position and GTID are not cloned : Implemented in MDEV-36751
5. Concurrent DDLs are blocked : Implemented in MDEV-36747
6. Clone runs single threaded. [performance] : Implemented in MDEV-36744

Development Note:
1. Prototype code from main-MDEV-35248 is to be used.
2. All related mtr tests must be ported from MySQL. Must work on all platforms(CI).
3. All relevant Maria Backup mtr test should be translated for clone.
3. Clone must be tested with concurrent sysbench load.
4. The review of the ported code can be started early as the majority of the ported code from MySQL .

QA/Test Note:
1. Should develop RQG test for Clone and concurrent DML test.