Support OpenAlex (soon required) API_KEY as URL parameter

[elya5]

OpenAlex plans to require API users to use an API key for more queries (see this post) which is passed via the URL e.g. https://api.openalex.org/works?api_key=424242 (see docs).

It seems that currently pyalex passes the API_KEY value via headers. This probably needs to be adapted for future compatibility.

[PeterLombaers]

Thanks for reporting this. I assume that the current way that PyAlex handles API keys (via headers) should also work in the future. The current way via headers is not documented on OpenAlex's side but does in fact work. If that's not the case after the update then PyAlex will be updated as quickly as possible to solve the issue.

I'll leave this issue open until the OpenAlex update. If everything still works then I'll close it.

[Guthman]

See: #100