Add logging transport to log HTTP requests in log level -3

The log level -3 is the minimum log level that is supported today, smaller than debug(-1) and -2(used to log some HRA related logs).

This commit adds a logging HTTP transport to log HTTP requests and responses to that log level.

It implements http.RoundTripper so that it can log each HTTP request with useful metadata like `from_cache` and `ratelimit_remaining`.
The former is set to `true` only when the logged request's response was served from ARC's in-memory cache.
The latter is set to X-RateLimit-Remaining response header value if and only if the response was served by GitHub, not by ARC's cache.

logging/logger.go

@@ -0,0 +1,54 @@
+package logging
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+
+	"github.com/go-logr/logr"
+	zaplib "go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+	"sigs.k8s.io/controller-runtime/pkg/log/zap"
+)
+
+const (
+	LogLevelDebug = "debug"
+	LogLevelInfo  = "info"
+	LogLevelWarn  = "warn"
+	LogLevelError = "error"
+)
+
+func NewLogger(logLevel string) logr.Logger {
+	log := zap.New(func(o *zap.Options) {
+		switch logLevel {
+		case LogLevelDebug:
+			o.Development = true
+			lvl := zaplib.NewAtomicLevelAt(zaplib.DebugLevel) // maps to logr's V(1)
+			o.Level = &lvl
+		case LogLevelInfo:
+			lvl := zaplib.NewAtomicLevelAt(zaplib.InfoLevel)
+			o.Level = &lvl
+		case LogLevelWarn:
+			lvl := zaplib.NewAtomicLevelAt(zaplib.WarnLevel)
+			o.Level = &lvl
+		case LogLevelError:
+			lvl := zaplib.NewAtomicLevelAt(zaplib.ErrorLevel)
+			o.Level = &lvl
+		default:
+			// We use bitsize of 8 as zapcore.Level is a type alias to int8
+			levelInt, err := strconv.ParseInt(logLevel, 10, 8)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Failed to parse --log-level=%s: %v", logLevel, err)
+				os.Exit(1)
+			}
+
+			// For example, --log-level=debug a.k.a --log-level=-1 maps to zaplib.DebugLevel, which is associated to logr's V(1)
+			// --log-level=-2 maps the specific custom log level that is associated to logr's V(2).
+			level := zapcore.Level(levelInt)
+			atomicLevel := zaplib.NewAtomicLevelAt(level)
+			o.Level = &atomicLevel
+		}
+	})
+
+	return log
+}