fix: Improve device icon serving

[Koenkk]

Currently device icons are stores as base64 string inside the device options. This significantly increases the size of the configuration.yaml, especially when done for all devices (which is what the localise device images on the frontend does). This can even lead to Zigbee2MQTT failing to start (e.g. #25259). With this PR device icons are now saved in the device_icons directory, the configuration.yaml only contains the reference to the image, e.g.:

devices:
    '0x847127fffe8d96bc':
        friendly_name: '0x847127fffe8d96bc'
        icon: device_icons/08a9016bbc0657cf5f581ae9c19c31a5.png

Note that images must be in the device_icons directory!

Fixes: #25259, nurikk/zigbee2mqtt-frontend#2100, nurikk/zigbee2mqtt-frontend#1477

TODO:

• Test with base url change
• Add check to settings
• Update docs: Device icons docs zigbee2mqtt.io#3352

[Nerivec]

Did you give this a try on Windows? Since it's dealing with file system.

[Koenkk]

I don't have a Windows machine to test on but the tests found an issue which I fixed in e46c2b6

[Koenkk]

Added a migration to automatically convert base64 icons to pngs and prohibited base64 in the configuration.yaml.

[Nerivec]

Tested it on Windows, image showed up without problem.

zigbee2mqtt/lib/util/settings.schema.json

Lines 804 to 808 in 62e18a6

	"icon": {
	"type": "string",
	"title": "Icon",
	"description": "The user-defined device icon for the frontend. It can be a full URL link to an image (e.g. https://SOME.SITE/MODEL123.jpg) (you cannot use a path to a local file) or base64 encoded data URL (e.g. image/svg+xml;base64,PHN2ZyB3aW....R0aD)"
	},

This description needs updating.

[Koenkk]

@Nerivec good point, I forgot that URLs are should also be supported!

[Koenkk]

thanks for the feedback, created #25364