Replaced doc.akka.io with pekko.apache.org (#120)

* modified all references in docs module

* replaced in inline scala docs

* renamed variable and changed access specifier

* reanmed in remaining places

* Adjusted path (instead of `akka` used `pekko`)

* Where applicable akka.io is replaced with pekko.apache.org

* replaced akka with pekko in the path

* Removed TODO

* Removed migration guide to gRPC (there is no user using pekko at the moment so no need of migration guide)

* Added back migration to gRPC section

* removed TODO

* alpakka is replaced with pekko-connectors

* the Akka online documentation -> the Pekko online documentation

* referring akka security docs

* reffering to akka migration guides (pekko is not managing them)

* Using pekkoBaseURL for platform-guide.base_url

* removed unnecessary redirects and used current instead of 2.6

* Changed akka discovery to pekko discovery

* Some more replacement

* fix merge issue

* revert platform-guide change because we

---------

Co-authored-by: PJ Fanning <pjfanning@users.noreply.github.com>

project/Doc.scala

@@ -70,11 +70,11 @@ object Scaladoc extends AutoPlugin {
       "-sourcepath",
       base.getAbsolutePath,
       "-doc-title",
-      "Akka",
+      "Apache Pekko",
       "-doc-version",
       ver,
       "-doc-canonical-base-url",
-      "https://doc.akka.io/api/akka/current/")
+      "https://pekko.apache.org/api/pekko/current/")
     CliOptions.scaladocDiagramsEnabled.ifTrue("-diagrams").toList ::: opts
   }
 
@@ -158,7 +158,7 @@ object UnidocRoot extends AutoPlugin {
         val releaseVersion = if (isSnapshot.value) "snapshot" else version.value
         (Compile / unidoc).value match {
           case Seq(japi, api) =>
-            Seq(japi -> s"www/japi/akka/$releaseVersion", api -> s"www/api/akka/$releaseVersion")
+            Seq(japi -> s"www/japi/pekko/$releaseVersion", api -> s"www/api/pekko/$releaseVersion")
         }
       }))
     .getOrElse(Nil)