Global gradle proxy settings?

Yes it seems possible. See here, especially:

We can define a gradle.properties file and set the property in this
file. We can place the file in our project directory or in the
<USER_HOME>/.gradle directory. The properties defined in the property
file in our home directory take precedence over the properties defined
in the file in our project directory. As a bonus we can also define
system properties in a gradle.properties file, we only have to prefix
the property name with systemProp..

The gradle.properties files can be found at the following paths:

# windows gradle file
%userprofile%\.gradle\gradle.properties

# linux gradle file
~/.gradle/gradle.properties