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/attributes.go

@@ -0,0 +1,24 @@
+package otel
+
+import (
+	"go.opentelemetry.io/otel/attribute"
+
+	fv1 "github.com/fission/fission/pkg/apis/core/v1"
+)
+
+/* GetAttributesForFunction returns a set of attributes for a function. Attributes returned:
+    function-name
+    function-namespace
+    environment-name
+    environment-namespace
+
+These attributes are tags that can be used to filter traces.
+*/
+func GetAttributesForFunction(fn *fv1.Function) []attribute.KeyValue {
+	return []attribute.KeyValue{
+		{Key: "function-name", Value: attribute.StringValue(fn.Name)},
+		{Key: "function-namespace", Value: attribute.StringValue(fn.Namespace)},
+		{Key: "environment-name", Value: attribute.StringValue(fn.Spec.Environment.Name)},
+		{Key: "environment-namespace", Value: attribute.StringValue(fn.Spec.Environment.Namespace)},
+	}
+}