Improve geocoding error handling e.g. timeout

Problem/Motivation

When testing geocoding using Photon yesterday it worked well, but today I encountered timeout issues.

The same error is present on https://photon.komoot.io/, so the problem must be in the API, but the error wasn't obvious to the user without digging into the browser console and the logs.

Steps to reproduce

1. set up a geocoding field (either with or without address field integration)
2. try to geocode without network connection to the API

Proposed resolution

Add an error message so that it's clear to the user that there's a problem with the API

Remaining tasks

User interface changes

API changes

Data model changes