Setup the release process

Apache has certain requirements for releasing a public version. We should strive for as much automation as possible. This ticket should be an overview over all steps necessary and the progress on those items. Please add items as needed.

Let's only consider public releases like RCs and GAs here (but not snapshots).

(Please add your name and/or PRs and issues to the items as needed)

References:
* [Apache Release Management](https://incubator.apache.org/guides/releasemanagement.html)
* [Apache Release Distribution Policy](https://infra.apache.org/release-distribution.html)
* [Apache Publishing Maven Artifacts](https://infra.apache.org/publishing-maven-artifacts.html)
* [Apache Release Signing](https://infra.apache.org/release-signing.html)

## Organizational steps
* [ ] Create release template to keep track progress of release process per release (see the old template at https://github.com/apache/incubator-pekko/blob/main/scripts/release-train-issue-template.md)
* [ ] Setup release managers (Who will it be?)

## Maven-related steps

* [ ] Publish to Apache Nexus into staging
* [ ] Initiate voting
* [ ] Propagate to Maven Central when vote is positive
* [ ] ...

## Apache-related steps

* [ ] (one-time) setup signing infrastructure (how are keys created, where can a release be signed)
* [ ] Create signed release and upload artifacts (where and when does that happen? Can signing keys be safely used from GHA?)
* [ ] ...