fix: create accessible gatlingScalafixWriteTask

Motivation:
Weird error when inspecting a task in sbt.

Modifications:
 * Use a public task instead of a private local one.

Result:
No more error in sbt when inspecting.
User may change this task implementation

src/main/scala/io/gatling/build/automated/GatlingAutomatedScalafixPlugin.scala

@@ -26,10 +26,9 @@ import sbt.{ Def, _ }
 object GatlingAutomatedScalafixPlugin extends AutoPlugin {
   override def requires: Plugins = ScalafixPlugin && GatlingBuildConfigPlugin
 
-  private val gatlingScalafixWriteTask = TaskKey.local[File]
-
   trait GatlingAutomatedScalafixKeys {
     val gatlingScalafixConfigFile = settingKey[File]("Location of the scalafix configuration file")
+    val gatlingScalafixWriteTask = taskKey[File]("write scalafix file")
 
     def automateScalafixBeforeCompile(configurations: Configuration*): Seq[Setting[_]] =
       configurations.toSeq.flatMap(