Rename db-discovery type

[terrymanu]

Hi, the current db-discovery type is MGR, MASTER_SLAVE and openGauss which are not in same abstract level and the case .

MGR and MASTER_SLAVE is for MySQL only, and openGauss is other db-discovery type of database, not HA method.

It is better to rename and standardize the db-discovery type. I prefer rename like the way below:

MGR -> MySQL.MGR
MASTER_SLAVE -> MySQL.NORMAL_REPLICATION
openGauss -> openGauss.NORMAL_REPLICATION

[zhaojinchao95]

I agree, that 's a good idea.

[terrymanu]

I will change it soon