Check and improve proxy support

[koettert]

The goal of this ticket is to ensure that all geospatial nodes use the newly available proxy settings. With AP-20960 that was released with KNIME AP 5.2 the Python framework sets the proxy information configured via the HTTP_PROXY and HTTPS_PROXY environment variables (via ~~os.setenv(...)~~ os.environ). In addition the proxy settings can be retrieved via knext.get_proxy_settings()

For debugging and testing we can use https://mitmproxy.org/ and Ask Adrian for help.

Steps to do:

1. Install and setup https://mitmproxy.org/ or any other tool to debug proxy usage
2. Setup the proxy in KNIME AP (needs to be version 5.2 or newer) by opening Preferences->General->Network Connections and then editing the http and https entries
3. Restart KNIME AP
4. Execute different Geospatial nodes especially the OSM nodes to see if they use the proxy settings or ignore it