This commit introduces a first simulator for read_only monitoring

ProxySQL itself will simulate hundreds of backends across hundreds of
hostgroups, all configured in hundreds of clusters, and return read_only
values for each of the simulated backend.
The read_only value can be configured in table READONLY_STATUS available in
the SQLite3Server module.

If a backend isn't configured in table READONLY_STATUS , its default read_only
value is 1.

It is possible to simulate a lot of simultaneous failover running queries like
the following:

UPDATE READONLY_STATUS SET read_only=1;
CREATE TABLE t1 AS SELECT hostname FROM READONLY_STATUS ORDER BY RANDOM() LIMIT 50;
UPDATE READONLY_STATUS SET read_only=0 WHERE hostname IN (SELECT hostname FROM t1);
DROP TABLE t1;

…providing proper waiting for 'SQLITE_BUSY'

…'ProxySQL_Admin::save_mysql_servers_runtime_to_database'

…d_only_action'

…ervers' and 'mysql_replication_hostgroups' from 'enable_readonly_testing'

…only_table'

This commit optimizes the read-only actions method by removing the dependency on proxysql admin tables. Instead, a separate mapping container is maintained, which records the state of the HGM servers. This avoids the need to call the commit method on every change, which improves performance.
The changes in this commit also ensure that the mapping container is properly updated when servers are added, removed or modified.

# Conflicts:
#	lib/MySQL_Monitor.cpp

…into v2.x_refactor_read_only_action_with_simulator

…nto v2.x_refactor_read_only_action_with_simulator

* Introduced support for handling of bulk servers
* Commented mysql_servers_wrlock as this method does not use admin tables.

…tion' into v2.x_refactor_replication_lag_action