Starting 18.104.22.168 Oracle creates a new mandatory database called MGMTDB, Oracle creates on it Cluster Health Monitoring (CHM) Data among others, this database gets failover to a surviving node in case one node goes down, the database needs to be up and running, it starts up automatically.
Please note: There is a minus sign in from of the database name
Database name: -MGMTDB
ORACLE_HOME: Same as the GRID_HOME
I am not sure about the password for SYS or SYSTEM on it, but you can connect as sysdba
There are 3 tablespaces on it (UNDO, SYSTEM and SYSAUX) , you do not have to worry about space management since the datafiles are auto-extensible.