added predicate fn to switch "Half Open" to "Open"

[Sandy10247]

Description

• Added predicate Fn "ReadyToOpen" for Settings and consumed it in CircuitBreaker initalization.
• Added defaultReadyToOpen fn implemetation, when parent won't provide one, this will be used as default behaviout.

usage

cfg := gobreaker.Settings{
		// When to flush counters int the Closed state
		Interval: 5 * time.Second,
		// Time to switch from Open to Half-open
		Timeout: 7 * time.Second,
		// Function with check when to switch from Closed to Open
		ReadyToTrip: shouldBeSwitchedToOpen,
		// set Max Request in Half Open state to 5
		MaxRequests: 5,
		// On State change Handler Fn
		OnStateChange: func(_ string, from gobreaker.State, to gobreaker.State) {
			// Handler for every state change. We'll use for debugging purpose
			logger.Println("state changed from", from.String(), "to", to.String())
		},
		ReadyToOpen: func(counts gobreaker.Counts) bool {
			fmt.Printf("Ready to open called\n")
			return true
		},
	}