Add automatic/scheduled update feature to ESPHome

At present, if an update is available, the user has to manually click the 'update all' button on the ESPHome dashboard. It would be advantageous if this update operation could be scheduled automatically. I am running esphome on a slowish system, the compile times are long and my device count high so it would be nice to automate this operation to occur overnight.

The issue mentions the ESPHome dashboard's “update all” button and overnight scheduling, but names no files or tests. Start by locating the dashboard update flow and determine how available updates and device compilation are represented. Done should mean users can configure an automatic schedule that performs the intended updates without manual interaction.

Written by the indexing model from the issue text.