Publish snapshots to GitHub packages

[bestbeforetoday]

As a contributor
I want snapshot versions of fabric-chaincode-shim to be published to GitHub Packages on every change
So that I can use development fixes or features before a formal release is published

The release.yml workflow already publishes to GitHub Packages (as well as Maven Central). It would be good for only the GitHub Packages publish to be done on every push.yml workflow. To differentiate from release versions, the Gradle package version used for the push workflow should be of the form x.y.z-SNAPSHOT. This is a standard Maven naming convention.

Although it uses Maven rather than Gradle, the CI pipeline for the fabric-gateway project could be used as a rough guide.