tools: enable auto-update of gopls by default

gopls is a central part of the extension, and staying up-to-date is critical for receiving important bug fixes, using the new features the new version of extension depend on, ... Some users already opted in to auto-update `gopls`.

Now consider to enable it by default. 
At minimum, we should be able to update it to the desirable version when a new version of Go extension is installed.