Update outdated links to scala-sbt.org in the documentation (backport #10918)

Update links to scala-sbt.org which were out of date

(cherry picked from commit 14dbd4a35ede1d7...

add explicit type annotations for implicit val and def

avoid deprecated scala.Either#right

update `unmanagedSourceDirectories` setting for Scala 3

- https://github.com/scala/scala/blob/v2.13.6/src/library/scala/util/Either.scala#L171-L172
- ht...

Small config + comments cleanup

For CI jobs, print files used by sbt + env vars

Remove obsolete CertificateGenerator

add explicit type annotations for public implicit val and def

fix procedure syntax warnings

fix Auto-application warnings

fix warnings. use slash syntax instead of old `in`

add parentheses for lambda param

align indent in `forwardsRouter.scala.twirl`

Remove routeAndCall(...) methods that depended on StaticRoutesGenerator

Use app materializer to execute action in akka-http backend

Prefer -agentlib:jdwp= over -Xrunjdwp:

specs2-core, specs2-junit, ... 4.12.0 (was 4.11.0)

htmlunit-driver 2.50.0 (was 2.49.1)

webjars-locator-core 0.47 (was 0.46)

sbt-mima-plugin 0.9.2 (was 0.9.0)

netty-transport-native-epoll 4.1.65.Final (was 4.1.63.Final)

mockito-core 3.11.1 (was 3.10.0)

spring-beans, spring-context, ... 5.3.8 (was 5.3.7)

sbt-jmh 0.4.3 (was 0.4.2)

Remove play-enhancer from docs, project is dead

Run tests against Scala 2.12.14 and 2.13.6 and sbt 1.5.3

avoid `Line is indented too far to the left` warning in Scala 3

prepare Scala 3

```
scala> Option(1).map{ a => a }
val res0: Option[Int] = Some(1)

scala> Opti...

Make sure scripted jobs use the same commit like publish-local did

https://github.com/sbt/sbt/commit/e6fec6b1db5f212a74bf5e3766b9b70f2d983f24
https://www.scala-sbt...

prepare Scala 3

Remove outdated line in travis.yml

scalacheck 1.15.4 (was 1.15.3)

spring-beans, spring-context, ... 5.3.7 (was 5.3.6)

sbt 1.5.2 (was 1.5.1)

sbt-jmh 0.4.2 (was 0.4.0)

specs2-core, specs2-junit, ... 4.11.0 (was 4.10.6)

ehcache 2.10.9.2 (was 2.10.6)

sbt-mima-plugin 0.9.0 (was 0.8.1)

mockito-core 3.10.0 (was 3.9.0)

caffeine, jcache 2.9.1 (was 2.9.0)

Remove bintray leftovers (fixes CRON build)

Fix reference.conf "router.Routes" FCQN comment

sbt 1.5.1