Nominatim search provider

[glughi]

What this PR does

Added search provider for Nominatim of OpenStreetMap

Checklist

• [ ] There are unit tests to verify my changes are correct or unit tests aren't applicable (if so, write quick reason why unit tests don't exist)
• [ ] I've updated relevant documentation in doc/.
• [x] I've updated CHANGES.md with what I changed.
• [ ] I've provided instructions in the PR description on how to test this PR.