Add ability to set a custom hostname

[mwood77]

To do:

• implement in BE
• restart ESP32 after setting
• prevent null from being set as hostname
• implement in FE (UI + warnings)
• implement in FE (logic)
• attach new FE artifacts (updated settings.json must be packaged into build!)

[mwood77]

Will not implement hostname modification as it's too complex for the average user - high likelihood of "losing" the winder on a user's local network. When lost, the only way to recover it is by completely wiping the device and starting new again.