+act #15502: Pluggable DNS resolution in akka-io
=con #15600 Fix config in PeekMailboxSpec
Merge pull request #15417 from hajile/master

+act #15502: Pluggable DNS resolution in akka-io
Merge pull request #15601 from LeonardMeyer/LMeyer-specfix-#15600

=con #15600 Fix config in PeekMailboxSpec
Add abbrev for project changes to CONTRIBUTING.md

As noticed during https://github.com/akka/akka/pull/15617, we didn't hint people to use `=pro` when changing things in the project / build.
=pro #15616 UTF-8 charset and exception with offending file (for Validation)
Merge pull request #15623 from ktoso/port-15616-master-ktoso

=pro #15616 UTF-8 charset and exception with offending file (for Validation)
=doc #15565 improved wording in cluster-usage docs
Merge pull request #15624 from ktoso/docs-cluster-joining-ktoso

=doc #15565 improved wording in cluster-usage docs
=con #15613 Rename one of the DistributedPubSubMediatorSpec classes
=doc Fix typo in scala remoting.rst
Merge pull request #15630 from savulchik/patch-1

Fix typo in scala remoting.rst
+con #13737 Interceptors chain for Actors' bahavior.

* Add new pattern to akka-contrib.
* Mixin ReceivePipeline trait into Actors that have to be intercepted.
Merge pull request #15629 from akka/wip-15613-rename-DistributedPubSubMediatorSpec-patriknw

=con #15613 Rename one of the DistributedPubSubMediatorSpec classes
Merge pull request #1869 from ktonga/wip-3737-interceptors-chain-for-receive-ktonga

#3737 Interceptors chain for receive