Adds configuration option to exclude the webserver on esp32.

[jimwhitelaw]

Followup to the suggestion by @caveman99 to make including the webserver optional on esp32. Excluding the webserver saves about 8kb of flash on the device and disables the web app and the TCP API. TCP (via wifi or ethernet) remains enabled for use by NTP or MQTT if needed. Tested with tbeam and tlora-v2-1-1_6 devices.

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[jimwhitelaw]

@caveman99, I'm not sure what I'm to do about these failing CI checks on files I haven't changed. Can you offer any insight? I've got some additional changes lined up to facilitate minimal builds using the pattern you've initiated (build w/o BT, Wifi, GPS) but I'm struggling to understand what mistake I'm making here. thx