duplicate fields cannot be defined in the mysqlConf of the MysqlCluster resource.

[usernameisnull]

MySQL allow duplicate field, likebinlog_do_db

[mysqld]
binlog_do_db            = db3
binlog_do_db            = db4
# other fields

in mysql we can get the result

mysql> show master status\G
*************************** 1. row ***************************
             File: binlog.000022
         Position: 157
     Binlog_Do_DB: db3,db4
 Binlog_Ignore_DB:
Executed_Gtid_Set:
1 row in set (0.00 sec)

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but in MysqlCluster resource, mysqlConf field is a map[string]string, not allowed to do this, if in IDE will warn us

spec:
  backupRemoteDeletePolicy: delete
  image: docker.m.daocloud.io/library/mysql:5.7.31
  mysqlConf:
    binlog-format: ROW
    binlog_do_db: db3
    binlog_do_db: db4

if we apply this cr, in running mysql,only one value

mysql> show master status\G
*************************** 1. row ***************************
             File: mysql-bin.000003
         Position: 154
     Binlog_Do_DB: db4
 Binlog_Ignore_DB:
Executed_Gtid_Set:
1 row in set (0.00 sec)