initial config without mqtt broker address results in unstable web ui

[Girgitt]

After initial config via web ui the main ui is unstable and M5Core2 reboots often making is very difficult to proceed with configuration.

Once mqttbroker value is set the interface becomes stable.

Minimum workaround is to extend initial config page in AP mode (http://192.168.99.1) with settings related to mqtt broker; at least the address.

[Girgitt]

reboots are related to
espressif/arduino-esp32#4647
knolleary/pubsubclient#794

There are no issues if mqttbroker URI is set correctly.