Add RunOption to overwrite the RunOpts in globals.GlobalOpts

[shawnh2]

Is your feature request related to a problem? Please describe.
Envoy Gateway standalone mode is using func-e to start envoy locally, we'd like to expose more RunOption in api/run.go. Especially the ability to override the RunOpts in global.GlobalOpts, eg customize our own RunOpts.RunDir.

Describe the solution you'd like
Add a new RunOption function that has ability to override global.GlobalOpts.RunOpts

Describe alternatives you've considered
Without this modification, we have to rewrite api/run.go completely on our own. We'd like to make this modification in the upstream.

Additional context
cc @arkodg

[codefromthecrypt]

Latest release has all directories configurable using XDG conventions!