New region for filters

[Claurt07]

Issue
New categories in the region filter are needed to describe those who are not part of a hub. Issue raised by Geoffrey K.

Solution proposed
We could add a category of "other"

Alternative solutions
Atlernatively have a deeper discussion on how we filter geographically, and thing about "mena", "europe", etc

Screenshots

[Tarekchehahde]

Opened PR: https://github.com/hotosm/website/pull/

Adds Other region filter for members without a mapping hub.