Profile mode with go-flutter

[Tokenyet]

Is your feature request related to a problem?

App/Software optimization

Describe the feature you'd like

hover run --profile or hover run --p

Recently, my app that met a memory problem when users open the app over 2 days, then 2 gb ram will be filled up. Since observatory's memory native profiler only supported in profile mode, let me here to request this feature :P

[pchampio]

Profile mode requires a special version of the flutter engine.
Profile/Release mode requires #259 to first be fixed.