[Go] GC spec

1. under 4MB memory consumption GC will not be triggered
2. between 2 garbage collecting more than 2 minutes, 1 GC cycle will be triggered.
3. heap threshold being reached GC will be triggered (100% memory bump) (env variable  GOGC set to 100)
4. Go garbage collector is to not take more than 25% of the CPU.
   i.e will use goroutine that is in idle queue to do the GC marking phase while the total counts of goroutine, which uses a P, is less than total counts of P.