Remove dependency on `sbt-dependency-graph`

[mkurz]

Turns out, this line

https://github.com/apache/incubator-pekko-http/blob/a6f2ff64a8a028b39a662b460da1ba4c1fe81105/project/plugins.sbt#L20

is not needed anymore since sbt 1.4, because it's build in now. See https://www.scala-sbt.org/1.x/docs/sbt-1.4-Release-Notes.html#sbt-dependency-graph+is+in-sourced

Actually for advanced usage you can replace it with

addDependencyTreePlugin

However it's not that easy, because you make use of apis here: https://github.com/apache/incubator-pekko-http/blob/a6f2ff64a8a028b39a662b460da1ba4c1fe81105/project/ValidatePullRequest.scala#L17-L18

which in sbt are now internal... (Maybe it's easy to fix, but didn't try, leave that up to you)

[mkurz]

Same story for akka-http:

• https://github.com/akka/akka-http/issues/4346

[mkurz]

Also:

• https://github.com/lightbend/sbt-paradox-dependencies/issues/34