Setup PGP signature for Embed CDT

Embed CDT will need to provide PGP signatures for its artifacts: https://github.com/eclipse-embed-cdt/eclipse-plugins/pull/648 Can you please setup PGP signatures and credentials on Jenkins and share the public key id to properly configure signing?

Same as #3070 (closed), but for iot.embed-cdt on https://ci.eclipse.org/embed-cdt/