[Python] Add new request types available in the OpenSky REST API.

[marataj]

I recently found the OpenSky service, and it's great! I used it in my private data analysis projects. So far I have mainly worked with the REST API, but decided to adapt the python library to all request types that were needed. During the work, the code has been tested on Python 3.10 and 2.7 to keep compatibility, as assumed. I'm happy to contribute to this project!

The scope of changes is the extension of the OpenSkyApi class with additional methods, that cover all types of requests available in the OpenSky REST API.

[jaluebbe]

To clarify how to use your new class/methods, you may create the documentation for https://openskynetwork.github.io/opensky-api/python.html by editing https://github.com/openskynetwork/opensky-api/blob/master/docs/free/python.rst .

[marataj]

To clarify how to use your new class/methods, you may create the documentation for https://openskynetwork.github.io/opensky-api/python.html by editing https://github.com/openskynetwork/opensky-api/blob/master/docs/free/python.rst .

Done.

[jaluebbe]

I looked into the documentation. It looks great. However, it is not clear where the user credentials are required and where not. Compare to the example for my states "api = OpenSkyApi(USERNAME, PASSWORD)".

[jaluebbe]

all tests passed on my machine.