For your question: "do I need to configure anything for users on oracle side?"
The privileges that you have to grant to the user are the following:
GRANT EXECUTE_CATALOG_ROLE TO [gcp_datastream_username];
GRANT CONNECT TO [gcp_datastream_username];
GRANT CREATE SESSION TO [gcp_datastream_username];
GRANT SELECT ANY TRANSACTION TO [gcp_datastream_user];
GRANT SELECT ANY TABLE TO [gcp_datastream_user];
exec rdsadmin.rdsadmin_util.grant_sys_object('V_$DATABASE','[gcp_datastream_user]','SELECT');
exec rdsadmin.rdsadmin_util.grant_sys_object('V_$ARCHIVED_LOG','[gcp_datastream_user]','SELECT');
exec rdsadmin.rdsadmin_util.grant_sys_object('V_$LOGMNR_LOGS','[gcp_datastream_user]','SELECT');
exec rdsadmin.rdsadmin_util.grant_sys_object('V_$LOGMNR_CONTENTS','[gcp_datastream_user]','SELECT');
exec rdsadmin.rdsadmin_util.grant_sys_object('DBMS_LOGMNR','[gcp_datastream_user]','EXECUTE');
exec rdsadmin.rdsadmin_util.grant_sys_object('DBMS_LOGMNR_D','[gcp_datastream_user]','EXECUTE');
This is needed ONLY if you are working with Oracle 12c or newer:
GRANT LOGMINING TO [gcp_datastream_user];