Controller info endpoint and API integration examples (#75)

* Controller API: introduce controller's information endpoint

* Prevent generation of empty events after channel closure

* Allow events to be buffered in the events channel

* Controller API: introduce controller's information endpoint[1]

* IntegrationGuide.md: a couple of Python and Golang examples

* Rephrase a sentence

Co-authored-by: Fedor Korotkov <fedor.korotkov@gmail.com>

---------

Co-authored-by: Fedor Korotkov <fedor.korotkov@gmail.com>

internal/controller/api_controller.go

@@ -0,0 +1,22 @@
+package controller
+
+import (
+	"github.com/cirruslabs/orchard/internal/responder"
+	"github.com/cirruslabs/orchard/internal/version"
+	v1pkg "github.com/cirruslabs/orchard/pkg/resource/v1"
+	"github.com/gin-gonic/gin"
+	"net/http"
+)
+
+func (controller *Controller) controllerInfo(ctx *gin.Context) responder.Responder {
+	// Only require the service account to be valid,
+	// no roles are needed to query this endpoint
+	if responder := controller.authorize(ctx); responder != nil {
+		return responder
+	}
+
+	return responder.JSON(http.StatusOK, &v1pkg.ControllerInfo{
+		Version: version.Version,
+		Commit:  version.Commit,
+	})
+}