Update executor contract, publish local dev server (#1385)

Author: mszostok

CONTRIBUTING.md

@@ -162,7 +162,7 @@ For faster development, you can also build and run Botkube outside K8s cluster.
 1. Start fake plugins server to serve binaries from [`dist`](dist) folder:
 
    ```bash
-   go run test/helpers/plugin_server.go
+   go run hack/target/serve-plugins/main.go
    ```
 
    > **Note**

hack/target/serve-plugins/main.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"flag"
+	"log"
+	"os"
+	"path/filepath"
+	"strconv"
+
+	"github.com/kubeshop/botkube/pkg/loggerx"
+	"github.com/kubeshop/botkube/pkg/plugin"
+)
+
+func main() {
+	pluginsDir := flag.String("plugins-dir", getEnv("PLUGINS_DIR", "plugin-dist"), "Plugins directory")
+	host := flag.String("host", getEnv("PLUGIN_SERVER_HOST", "http://localhost"), "Local server host")
+	port := flag.String("port", getEnv("PLUGIN_SERVER_PORT", "3010"), "Local server port")
+	flag.Parse()
+
+	dir, err := os.Getwd()
+	loggerx.ExitOnError(err, "while getting current directory")
+
+	portInt, err := strconv.Atoi(*port)
+	loggerx.ExitOnError(err, "while casting server port value")
+
+	binDir := filepath.Join(dir, *pluginsDir)
+	indexEndpoint, startServerFn := plugin.NewStaticPluginServer(plugin.StaticPluginServerConfig{
+		BinariesDirectory: binDir,
+		Host:              *host,
+		Port:              portInt,
+	})
+
+	log.Printf("Service plugin binaries from %s\n", binDir)
+	log.Printf("Botkube repository index URL: %s", indexEndpoint)
+	err = startServerFn()
+	loggerx.ExitOnError(err, "while starting server")
+}
+
+func getEnv(key, defaultValue string) string {
+	value, exists := os.LookupEnv(key)
+	if !exists {
+		return defaultValue
+	}
+	return value
+}