Plugin should inherit global proxy settings

[breedloj]

Is your feature request related to a problem? Please describe.
Customers with transparent proxies, or proxies that are configured globally at the operating system level, report frustration at having to explicitly configure proxy settings within the extension's preferences.

Describe the solution you'd like
In general the plugin should be able to inherit global proxy configurations wherever possible. The mechanism for configuring, and for retrieving said configuration, will likely differ by OS. It is also paramount to consistently apply proxy configuration to both the Eclipse and Flare components and that a clear configuration hierarchy is established and communicated to users (e.g., settings set in the plugin configuration always take precedence).

Describe alternatives you've considered
To date we've made a number of improvements to proxy configuration within the plugin itself, including the ability to set environment variables for proxy endpoint and CA cert, as well as #294 which allows for graphical configuration within the plugin's preference pane. While these changes make it possible to configure and run behind proxies, they still introduce inconvenience or challenges where users are unable to retrieve their global proxy configuration.