Set proper User-Agent

[joker234]

Ideally, ohsome-py should identify itself when doing requests. I would suggest to add a default user agent to any request (including the metadata requests) named ohsome-py/version, e.g. ohsome-py/0.1.0rc1. This version string could come from the pyproject.toml. If necessary, it could be allowed to set the user agent for the user of ohsome-py.

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