This commit fixes the missing pieces in our Maven Central publication
pipeline. Our first attempt at releasing with it showed a few problems:
* the promote task did not have the artifacts downladed with the
artifactory repository
* we applied the wrong Sonatype credentials to the task
* the github changelog task would fail because of docker rate limiting
since we were not using the right type of resource, which is
configured with the proper caching mechanism
See gh-26654
This commit skips the Bintray-related tasks in our CI pipeline and
instead relies on Maven Central for publishing Spring Framework
artifacts.
This commit also updates the CI pipeline to sign the artifacts directly
with the `artifactory-resource`.
Closes gh-26654
This commit adds new tasks to the release pipeline, generating release
notes automatically using the issues in the current milestone and
pushing that as the content of the GitHub release.
Closes gh-25922
Brian Clozel
Stephane Nicoll