[flagd] improve wait logic to a more elegant solution

[aepfli]

Our current waiting logic could be improved. It is a working wait logic, but it might not be the most elegant solution.

java-sdk-contrib/providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/resolver/common/Util.java

Lines 26 to 38 in cd0ea9e

	public static void busyWaitAndCheck(final Long deadline, final Supplier<Boolean> connectedSupplier)
	throws InterruptedException {
	long start = System.currentTimeMillis();
	do {
	if (deadline <= System.currentTimeMillis() - start) {
	throw new GeneralError(String.format(
	"Deadline exceeded. Condition did not complete within the %d " + "deadline", deadline));
	}
	Thread.sleep(50L);
	} while (!connectedSupplier.get());
	}

This task aims to migrate to an approach with notify() and wait(). As suggested by @chrfwow within #1115.