feat: add a warning icon to OTA page for battery devices when battery is too low to safely run an update

[Ricc68]

If the battery of a battery powered device is too low to safely complete a firmware update there's no information on the OTA page.
I've got this same situation with my devices and I did not notice that battery was too low because I went straight to the OTA page.
See my conversation with @Nerivec in #27098.

The icon is shown only when the battery is < 50% or is low or is battery_low.
I wanted to keep the code as much clean as possible so I have implemented a PowerSourceOTA that renders the danger icon.
The icon is not a red battery icon but a red circle with exclamation mark because I did not want to confuse the user with a red battery icon in this page when, for example at 49%, the icon in the device-page is dark grey indicating normal status of the battery.
Hoovering with the mouse over the icon shows a clear explanation message.
I have called the icon rendering at the end of the device line in the OTA page only if :

• the device is a battery device
• the above conditions are met
• a firmware update is available for that device

In all other conditions the icon is not rendered.

The example page looks like this:

@Nerivec @Koenkk @nurikk please review and comment what can be done better or requires more attention on my side.

[Ricc68]

I thought that the warning icon is better than the danger icon in this scenario as actually we are just issuing a warning.
The icon looks less scary but still informative:

[Koenkk]

@Nerivec does it make sense for this to go in https://github.com/Nerivec/zigbee2mqtt-windfront?

[Nerivec]

Yes, I planned on adding something similar too.