Add example images to `smoothness` field

[tordans]

The smoothness key shows a text list of answer right now (see id-tagging-schema).

It would be great to improve the usability and data quality by extending this list. For reference, check out what StreetComplete is working on in streetcomplete/StreetComplete#3617.

Ideally, the UI would…

• show a list of answer options based on the values of the surface key
• show the image right in place with the text, similar to what SC does
• show a 1 sentence intro text that scopes the answer, similar to what SC does

Thinks that we need to think about IMO

• create a new UI
• I think that would be the first field that is dependent on another fields value; also there is the fallback case when surface is not present, yet.
• probably extend the schema-builder so that we can add images and other text to the id-tagging-schema
• maybe use a shared reference source for the list, see idea at Extract surface and smoothness example image list in shared repository streetcomplete/StreetComplete#3592

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Related to this, #8548 would be great to have as well. Maybe as part of this new UI, we can show a small indicator on the field about the check_date.