retries: Create minimal demo of the Retry feature

[shalier]

With #3338 we proposed the creation of a POC of RetryPolicy.

This GitHub issue is for the creation of a demo, which can showcase this feature.

Create a demo to show the retry feature
See doc for additional info.

In our current demo we utilize a Bookstore app. This is an HTTP server, which responds to HTTP GET requests from another app called Bookbuyer.
To demo this feature we could:

1. Deliberately introduce errors in the Bookstore server. For example we could return a 500 ISE on every other request here:

   osm/demo/cmd/bookstore/bookstore.go

   Lines 91 to 115 in 9332db2

   	// sellBook increments the value of the booksSold
   	func sellBook(w http.ResponseWriter, r *http.Request) {
   	fmt.Println("Selling a book!")
   	atomic.AddInt64(&booksSold, 1)
   	setHeaders(w)
   	renderTemplate(w)
   	log.Info().Msgf("%s; URL: %q; Count: %d\n", getIdentity(), html.EscapeString(r.URL.Path), booksSold)
   	// Loop through headers
   	for name, headers := range r.Header {
   	name = strings.ToLower(name)
   	for _, h := range headers {
   	log.Info().Msgf("%v: %v", name, h)
   	}
   	}
   	go common.RestockBooks(1) // make this async for a smoother demo
   	// Slow down the responses artificially.
   	maxNoiseMilliseconds := 750
   	minNoiseMilliseconds := 150
   	intNoise := rand.Intn(maxNoiseMilliseconds-minNoiseMilliseconds) + minNoiseMilliseconds // #nosec G404
   	pretendToBeBusy := time.Duration(intNoise) * time.Millisecond
   	log.Info().Msgf("Sleeping %+v", pretendToBeBusy)
   	time.Sleep(pretendToBeBusy)
   	}

2. Then we can annotate the demo TrafficTarget to enable retry:

   osm/demo/deploy-traffic-target.sh

   Lines 9 to 14 in 707593c

   	kind: TrafficTarget
   	apiVersion: access.smi-spec.io/v1alpha3
   	metadata:
   	name: bookbuyer-access-bookstore-v1
   	namespace: "$BOOKSTORE_NAMESPACE"
   	spec:

3. Given that every other request is erroring out - we should not see errors in Bookbuyer app's logs

[shashankram]

Demo for Retry feature should go into https://main--osm-docs.netlify.app/docs/demos/