support the Secret Service API

It would great if on Linux we could support the [Secret Service API](https://specifications.freedesktop.org/secret-service/latest) (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 https://github.com/swiesend/secret-service/discussions/70

_Originally posted by @mkurz in https://github.com/apache/pekko/issues/3397#issuecomment-5129078694_

This relates to the in-memory key store in https://github.com/apache/pekko/blob/a81f3b1a6fff6fe84fef537783583871aa02facc/remote/src/main/scala/org/apache/pekko/remote/artery/tcp/ssl/PemManagersProvider.scala#L39

Start with remote/src/main/scala/org/apache/pekko/remote/artery/tcp/ssl/PemManagersProvider.scala, especially the in-memory key store reference. Read the Secret Service API specification and compare the two linked Java projects' D-Bus access approaches. Done means Pekko can support the Secret Service API on Linux for this key-store use case.

Written by the indexing model from the issue text.