Mongodb issues

Moved from: ZBXNEXT-5869
1. {MongoDB node by Zabbix Agent 2:mongodb.rs.state[

].change()}=1

diff() instead of change()

2. Preload metrics seem to be not available
Add error handling

3. added second override to Replication discovery (as replication lag is ever growing on arbiter, as arbiter is not replicating data and it is causing false alarm)