Include 'reproducible builds' sbt plugin (#26546)

This does 2 things:
* publish a 'buildinfo' report along with the project artifacts to describe
the build context and parameters
* post-process the jars to remove 'arbitrary' differences, such as jar file
ordering and timestamps.

This makes it easier to detect and explain when 2 builds of the same source
don't produce a bit-per-bit identical result. This for example can improve
our confidence that our distribution pipeline has not been compromised.

build.sbt

@@ -522,6 +522,7 @@ lazy val discovery = akkaModule("akka-discovery")
 
 def akkaModule(name: String): Project =
   Project(id = name, base = file(name))
+    .enablePlugins(ReproducibleBuildsPlugin)
     .settings(akka.AkkaBuild.buildSettings)
     .settings(akka.AkkaBuild.defaultSettings)
     .enablePlugins(BootstrapGenjavadoc)