Add info about which gpg signing keys will be used for published artifacts.

Looks like version 4.12 was published with key D477D51812E692011DB11E66A6EA2E2BF22E0543 ?

For security purposes, it would be great if you were able to publish details (in the project docs) about gpg public keys that are "valid" for use when verifying signing artifacts uploaded to maven central.

This allows for "out of band" verification of the expected signing key.

Some examples of other libs publishing their signing keys:

https://square.github.io/okhttp/security/security/#verifying-artifacts
https://docs.couchbase.com/java-sdk/current/project-docs/sdk-release-notes.html#verifying-artifacts

https://github.com/eclipse/jetty.project/blob/jetty-10.0.x/KEYS.txt
https://downloads.apache.org/commons/KEYS
https://downloads.apache.org/logging/KEYS

https://github.com/cbeust/jcommander/blob/4b97c3440347bedb79e374408b8f123cf0ff4fd4/SECURITY.md#gpg-signature-validation

These keys can be used with Gradle "Dependency verification"

See example of real world usage here:

• https://github.com/androidx/androidx/blob/androidx-main/gradle/verification-keyring.keys
• https://github.com/androidx/androidx/blob/androidx-main/gradle/verification-metadata.xml