Add ref key to natural=tree moreFields

[gy-mate]

Description, Motivation & Context

Several local governments operate tree cadastres which involves assigning IDs to trees maintained by them. This makes it easier to report ill or dead trees.

• Vienna: https://www.wien.gv.at/umweltgut/public/grafik.aspx?ThemePage=11
• Budapest: https://infogardenweb.hu/bpfatar/
• Zürich: https://www.maps.stadt-zuerich.ch/zueriplan3/Stadtplan.aspx?#route_visible=true&basemap=Stadtplan&map=&scale=8000&xkoord=2683299&ykoord=1247363&lang=&layer=Stadtbaum%3A%3A17&window=&selectedObject=&selectedLayer=&toggleScreen=&legacyUrlState=&drawings=
• Melbourne: https://www.theatlantic.com/technology/archive/2015/07/when-you-give-a-tree-an-email-address/398210/
• Amt Spreenhagen: https://data.europa.eu/data/datasets/be76a11b-1dd2-45bc-bac0-e57dd8b53de4?locale=en

Related issues

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Links and data

Relevant OSM Wiki links:

• https://wiki.openstreetmap.org/wiki/Tag:natural%3Dtree

Relevant tag usage stats:

https://taginfo.openstreetmap.org/tags/natural=tree#combinations

[github-actions]

🍱 You can preview the tagging presets of this pull request here.

[gy-mate]

Test-Documentation

Preview links & Sidebar Screenshots

https://pr-1398--ideditor-presets-preview.netlify.app/id/dist/#background=Bing&disable_features=boundaries&id=n11827671775&locale=en&map=19.76/47.48987/19.04705

Search

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Info-i

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Wording

• American English N/A
• name, aliases (if present) use Title Case N/A
• terms (if present) use lower case, sorted A-Z N/A

[gy-mate]

@tordans Could you please review this? Many thanks in advance! :)

[gy-mate]

@tyrasd Could you please review this PR? Many thanks in advance!