[demo] add secondary memorial:addr:* field for when the subtag schema is used

[tyrasd]

for #964 (this PR is not meant to be merged, it's just to get the demo/preview of the below mentioned functionality)

I tried adding both variants and make it that the UI picks the right one based on existing tags. However, the type:address does not allow other tags that addr:* (it does not automatically use a different prefix), so that was a dead end.

Something like this should do the trick. It's not 100% waterproof, as it relies on the memorial:addr:housenumber tag to determine which field to display (there might be the case where only be a memorial:addr:housename exists), but except for that it seems to work fine.

[github-actions]

🍱 Preview the tagging presets of this pull request here: https://pr-971--ideditor-presets-preview.netlify.app/id/dist/#locale=en.

[tordans]

Thanks a lot @tyrasd I merged this into #964. This PR can be closed IMO.