macOS product packaging improvements

Changes to consider:

• Use the Eclipse CBI macOS notarization service.
  • For more info, see: https://github.com/eclipse-cbi/macos-notarization-service
  • For instructions, see: https://wiki.eclipse.org/IT_Infrastructure_Doc#macOS_Notarization
  • For an example from Eclipse CommaSuite: https://gitlab.eclipse.org/eclipse/comma/comma/-/blob/main/org.eclipse.comma.standard.product/pom.xml#L144
  • Requires cbi-snapshots repository (as it is not yet released). For an example from Eclipse CommaSuite: https://gitlab.eclipse.org/eclipse/comma/comma/-/blob/main/pom.xml#L32
  • Release review (1.1.0): https://projects.eclipse.org/projects/technology.cbi/reviews/macos-notarization-service-1.1.0-release-review
  • Given the issues with notarizing JustJ 11.0.2, see #31 (comment 10847), we'll add notarization, but disable it, to be enabled at a later time, as part of #91 (closed).
• Add entitlements file (which we already configured, but didn't add)
  • For an example from Eclipse CommaSuite: https://gitlab.eclipse.org/eclipse/comma/comma/-/blob/main/org.eclipse.comma.standard.product/application.entitlement
• Package as .dmg file
  • For an example from Eclipse CommaSuite: https://gitlab.eclipse.org/eclipse/comma/comma/-/blob/main/org.eclipse.comma.standard.product/pom.xml#L127

All this should make sure that 'open anyway' isn't needed anymore. We should test it and update the installation instructions.

Note that according to the developers of Eclipse CommaSuite, this all works with JustJ JDK 15, but not yet JustJ JDK 11, as JustJ 11 not properly signed.