Add info about backup plugins to support bundle

Currently, we print info about:

• active plugins - https://github.com/jenkinsci/support-core-plugin/blob/master/src/main/java/com/cloudbees/jenkins/support/impl/AboutJenkins.java#L110
• disabled plugins - https://github.com/jenkinsci/support-core-plugin/blob/master/src/main/java/com/cloudbees/jenkins/support/impl/AboutJenkins.java#L111
• failed plugins - https://github.com/jenkinsci/support-core-plugin/blob/master/src/main/java/com/cloudbees/jenkins/support/impl/AboutJenkins.java#L112

It would also be useful to display info about backup plugin versions.

See https://github.com/jenkinsci/jenkins/blob/master/core/src/main/java/hudson/PluginWrapper.java#L1039