support the Secret Service API

[pjfanning]

It would great if on Linux we could support the Secret Service API (KDE also finally is removing kwallet and now supports the API already).

Quick online research found two Java project to access the API (which in the end are "just" d-bus calls):

• https://github.com/swiesend/secret-service
• https://github.com/purejava/secret-service

I also opened swiesend/secret-service#70

Originally posted by @mkurz in #3397 (comment)

This relates to the in-memory key store in

pekko/remote/src/main/scala/org/apache/pekko/remote/artery/tcp/ssl/PemManagersProvider.scala

Line 39 in a81f3b1

private[ssl] def buildKeyManagers(

[pjfanning]

I don't think we'd want any existing pekko jar to end up with a new dependency but we could possibly support adding an optional dependency.