Changes

PGP sign p2 artefacts

This ensures bundles directly pulled from Maven Central are PGP signed
by Tycho.

See https://docs.google.com/document/d/1MnDBvOUwKvKacB-QKnH_PzK88dUlHkjs-D-DWEKmvkY
and https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/issues/3078

Change-Id: I69c325bcc7cbc405a33460330bd7a5ad3f179bdc