MySQL asynchronous replication between 2 percona clusters doesn't work

As it was described in the bug https://bugs.launchpad.net/charm-percona-cluster/+bug/1934680 if we set databases-to-replicate as described in the upstream charm documentation [1]. This option turns on a number of MySQL options, like [2] that enable asynchronous replication, but it breaks Galera cluster replication.

To overcome that limitation we decided to replicate from Galera cluster to a single percona-cluster unit, but we're still seeing a few issues with the replication:

1) asynchronous replication between the clusters that have members with equal server-id may fail during 'START SLAVE' with errror like this:
Fatal error: The slave I/O thread stops because master and slave have equal MySQL server ids; these ids must be different for replication to work (or the --replicate-same-server-id option must be used on slave but this does not always make sense; please check the manual before using it).

2) max_allowed_packet might be too low and prevent certain transaction to go through

[1] https://jaas.ai/percona-cluster
[2] https://bugs.launchpad.net/charm-percona-cluster/+bug/1897274