Fixed Watch start button to show stop button once watch has started

[jinapurapu]

[kaankabalak]

@jinapurapu, if we want to save space, we can alternatively use the ternary operator as follows:

            {start ? (
              <Button
                type="submit"
                variant="contained"
                color="primary"
                onClick={() => setStart(false)}
              >
                Stop
              </Button>
            ) : (
              <Button
                type="submit"
                variant="contained"
                color="primary"
                onClick={() => setStart(true)}
              >
                Start
              </Button>
            )}

So, if the start condition is true, we'll render the Button that says Stop and if the start condition is false, we would render the Button that says Start