Add context.Context to Logger interface

This allows custom logger adapters to add additional fields to log
messages. For example, a HTTP server may with to log the request ID.

fixes #428

log/testingadapter/adapter.go

@@ -3,6 +3,7 @@
 package testingadapter
 
 import (
+	"context"
 	"fmt"
 
 	"github.com/jackc/pgx/v4"
@@ -22,7 +23,7 @@ func NewLogger(l TestingLogger) *Logger {
 	return &Logger{l: l}
 }
 
-func (l *Logger) Log(level pgx.LogLevel, msg string, data map[string]interface{}) {
+func (l *Logger) Log(ctx context.Context, level pgx.LogLevel, msg string, data map[string]interface{}) {
 	logArgs := make([]interface{}, 0, 2+len(data))
 	logArgs = append(logArgs, level, msg)
 	for k, v := range data {