Need to be able to set a user-agent for overpass-api.de

[arminus]

As of ~ April 18, overpass-api.de requires a user-agent to be set on each request, see drolbr/Overpass-API#791 (comment)

Presently, this doesn't seem to be supported by the overpy wrapper.

[welcome]

Thanks for opening your first issue here! Be sure to follow the issue template!