Set proper User-Agent

Ideally, ohsome2x should identify itself when doing requests. I would suggest to add a default user agent to any request (including the metadata requests) named ohsome2x/version, e.g. ohsome2x/2.5.2. This version string could come from the packages definiton. If necessary, it could be allowed to set the user agent for the user of ohsome2x (e.g. when used in larger projects).

Further information on the User-Agent: https://datatracker.ietf.org/doc/html/rfc7231#section-5.5.3

See also https://github.com/GIScience/ohsome-py/issues/72.