Add golangci-lilnt to CI (#1794)

This introduces a linter to PRs to help with code reviews and code hygiene. I've also gone ahead and fixed (or ignored) the existing lints.

I've only setup the default linters right now. There are many more options that are documented at https://golangci-lint.run/.

The GitHub Action should add appropriate annotations to the lint job for the PR. Contributors can also lint locally using `make lint`.

controllers/horizontal_runner_autoscaler_webhook.go

@@ -20,7 +20,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"strings"
 	"sync"
@@ -75,10 +75,8 @@ type HorizontalRunnerAutoscalerGitHubWebhook struct {
 	// A scale target is enqueued on each retrieval of each eligible webhook event, so that it is processed asynchronously.
 	QueueLimit int
 
-	worker      *worker
-	workerInit  sync.Once
-	workerStart sync.Once
-	batchCh     chan *ScaleTarget
+	worker     *worker
+	workerInit sync.Once
 }
 
 func (autoscaler *HorizontalRunnerAutoscalerGitHubWebhook) Reconcile(_ context.Context, request reconcile.Request) (reconcile.Result, error) {
@@ -133,7 +131,7 @@ func (autoscaler *HorizontalRunnerAutoscalerGitHubWebhook) Handle(w http.Respons
 			return
 		}
 	} else {
-		payload, err = ioutil.ReadAll(r.Body)
+		payload, err = io.ReadAll(r.Body)
 		if err != nil {
 			autoscaler.Log.Error(err, "error reading request body")