Plugin is not using global proxy configuration

Hi, we are using our Jenkins behind a firewall with no direct access to internet. However we have proxy configured in the plugins section. Other plugins read the proxy configuration from there but looks like the GKE plugin is not doing it. When it tries to connect with Google cloud we get some connection error.

Start by locating the plugin's Google Cloud connection entry point and how Jenkins global proxy settings are accessed. Reproduce the connection failure in a Jenkins instance behind a proxy, then verify that GKE connections use the configured proxy and succeed without direct internet access.

Written by the indexing model from the issue text.