Add FAQ with common problems to the User Guide

[ml-sudocode]

If there were an FAQ here, it would save your support people a lot of time https://docs.namada.net/users

A common question to be answered: "I cannot see xxx function on the interface / xx function stopped working and has been suspended. what do i do?" Answer(?): try a different interface. Sometimes for different reasons certain features go down. List of interfaces: https://namada.community/infra/interfaces