Fission meets OpenTelemetry (#2157)

* add opentracing section and otelCollectorEndpoint
* initialize OTLP exporter
* pkg/controller: changes for context propagation
* pkg/executor: changes for context propagation
* pkg/fetcher: changes for context propagation
* pkg/router: changes for context propagation
* pkg/storagesvc: changes for context propagation
* set no default value for otel collector endpoint
* update readme and add notes to charts
* move common code to pkg/utils/otel
* adding fn and env as attributes
* don't use otelhttp transport for websocket
* URL ignore with common filter UrlsToIgnore

Note: The web socket example does not work when using OTEL HTTP. Here is an issue related to that on open-telemetry/opentelemetry-js-contrib.

Signed-off-by: Gaurav Gahlot <gauravgahlot0107@gmail.com>
Co-authored-by: Sanket Sudake <sanketsudake@gmail.com>

pkg/utils/otel/handler.go

@@ -0,0 +1,31 @@
+package otel
+
+import (
+	"net/http"
+	"strings"
+
+	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
+)
+
+func UrlsToIgnore(ignoreEndpoints ...string) func(r *http.Request) bool {
+	return func(r *http.Request) bool {
+		for _, ignore := range ignoreEndpoints {
+			if strings.HasPrefix(r.URL.Path, ignore) {
+				return false
+			}
+		}
+		return true
+	}
+}
+
+func GetHandlerWithOTEL(h http.Handler, name string, filter ...otelhttp.Filter) http.Handler {
+	opts := []otelhttp.Option{
+		otelhttp.WithMessageEvents(otelhttp.ReadEvents, otelhttp.WriteEvents),
+	}
+
+	for _, f := range filter {
+		opts = append(opts, otelhttp.WithFilter(f))
+	}
+
+	return otelhttp.NewHandler(h, name, opts...)
+}