fix: issues found by M5 release verification

[jdaugherty]

Some initial feedback on the release has revealed the need for the following:

1. better document the signing requirement of a release version and how to override it
2. updates RELEASE.md to clarify manual steps vs the automated version of verify.sh
3. better document the dockerfile to handle platform differences in reproducible build testing
4. better document failure scenarios with the wrapper
5. if signing / release is enabled, still support publishing to the test case repo
6. eliminate a race condition on the test case repo publishing by moving the task to the grails gradle plugin
7. add validations to the publish plugin for when signing has been incorrectly configured