ESP32: Hostname replacement - Allow to change the original hostname to search for

[SciLor]

If people are flashing the box for a second time, the replacement of the hostname fails. The Frontend does not know, that the replacement failed.

There should be an option in the Frontend, where the user can select "I have already changed the hostname" and then be presented a text field to enter the changed hostname.

https://forum.revvox.de/t/changed-teddycloud-ip-esp32-can-not-connect-anymore-codewort-ant/1059/2

This should be combined with following to automatically detect that.
toniebox-reverse-engineering/teddycloud#270

[henryk86]

Add the backend for that an I will add that :)