Aggiungere pulsante pause/play a slideshow

[Cosina]

Buonasera a tutti, chiedo aiuto per aggiungere un pulsante, ad uno slideshow in javascript con autoplay, che permetta di fermarlo e di riavviarlo manualmente. Grazie mille. Il codice è il seguente:

*, *:before, *:after {
  -webkit-box-sizing: border-box;
  -o-box-sizing: border-box;
  box-sizing: border-box;
}

img {
  max-width: 100%;
}
/* Slideshow container */
.slideshow-container {
  max-width: 800px;
  position: relative;
  margin: 40px auto;
  width: 100%;
  overflow: hidden;
}

.slideshow-nav {
  text-align: center;
  width: 100%;
  position: absolute;
  bottom: 2%;
}

.mySlides {
  width: auto;
}
 
/* The dots/bullets/indicators */
.dot {
  height: 13px;
  width: 13px;
  margin: 0 2px;
  background-color: #f9f6f6;
  border-radius: 50%;
  display: inline-block;
  transition: background-color 0.6s ease;
}

.active, .dot:hover {
  background-color: #ff0000;
}

/* Next & previous buttons */
.prev, .next {
  cursor: pointer;
  position: absolute;
  top: 50%;
  padding: 6px;
  color: #fff;
  color: rgba(255, 255, 255, 0.5);
  font-weight: bold;
  font-size: 3.0rem;
  border-radius: 0 3px 3px 0;
  -webkit-transform: translateY(-50%);
  -ms-transform: translateY(-50%);
  transform: translateY(-50%);
  -webkit-transition: 0.6s ease-out;
  -moz-transition: 0.6s ease-out;
  -o-transition: 0.6s ease-out;
  transition: 0.6s ease-out;
}

/* Position the "next button" to the right */
.next {
  right: 0;
  border-radius: 3px 0 0 3px;
}

.prev:hover, .next:hover {
  background-color: black;
  color: white;
  cursor: pointer;
}

.fadeIn {
  -webkit-animation-name: fadeIn;
  animation-name: fadeIn;
  -webkit-animation-duration: 1s;
  animation-duration: 1s;
  -webkit-animation-fill-mode: both;
  animation-fill-mode: both;
}

@-webkit-keyframes fadeIn {
  0% {
    opacity: 0;
  }

  100% {
    opacity: 1;
  }
}

@keyframes fadeIn {
  0% {
    opacity: 0;
  }

  100% {
    opacity: 1;
  }
}

<!-- start slider -->
      <div class="slideshow-container">
         <!--Slide 1-->
         <div class="mySlides fadeIn">
            <img src="01.jpg">
         </div>
         <!--Slide 2-->
         <div class="mySlides fadeIn">
            <img src="02.jpg">
         </div>
         <!--Slide 3-->
         <div class="mySlides fadeIn">
            <img src="03.jpg">
         </div>
         <!--Silde 4-->
         <div class="mySlides fadeIn">
            <img src="04.jpg">
         </div>
         <a class="prev" onclick="plusSlides(-2);">❮</a>
         <a class="next" onclick="plusSlides(0)">❯</a>
         <div class="slideshow-nav">
            <span class="dot" onclick="currentSlide(0)"></span>
            <span class="dot" onclick="currentSlide(1)"></span>
            <span class="dot" onclick="currentSlide(2)"></span>
            <span class="dot" onclick="currentSlide(3)"></span>
         </div>
      </div>

var slideIndex = 1;
  var millis = 5000;
  var interval;
  var timeout;

  startSlides();
  function startSlides(){
    pauseSlides();
    nextSlide();
    interval = setInterval(nextSlide, millis);
  }
  function resumeSlides() {
    nextSlide();
  }
  function pauseSlides() {
    clearInterval(interval);
  }
  function nextSlide() {
    showSlide();
    slideIndex++;
  }
  function plusSlides(n) {
    clearInterval(interval);
    clearTimeout(timeout);
    slideIndex += n;
    nextSlide();
    timeout = setTimeout(startSlides, millis * 2)
  }
  function currentSlide(n) {
    clearInterval(interval);
    slideIndex = n + 1;
    nextSlide();
    interval = setInterval(nextSlide, millis);
  }
  function showSlide() {
    var i;
    var slides = document.getElementsByClassName("mySlides");
    var dots = document.getElementsByClassName("dot");
    for (i = 0; i < slides.length; i++) {
      slides[i].style.display = "none";
    }
    if (slideIndex > slides.length) {
      slideIndex = 1;
    }
    if (slideIndex < 1) {
      slideIndex = slides.length;
    }
    for (i = 0; i < dots.length; i++) {
      dots[i].className = dots[i].className.replace(" active", "");
    }
    slides[slideIndex - 1].style.display = "block";
    dots[slideIndex - 1].className += " active";
  }