Make key/value fields autocomplete via taginfo sugges

[tyrasd]

Make key/value fields autocomplete via taginfo suggestions api.
(idea by Oleksiy Muzalyev via osm-talk)

[tilmanb]

Do we need approval from taginfo maintainers for this?

I know that Nominatim explicitly forbids implementing type ahead search using the public API, I could not find such a restriction on the public taginfo API.