[JENKINS-40700] Enhance slave protocol descriptions

Relates to [JENKINS-40700].  The updated displayNames describe the
protocols by using similar verbiage from:

core/src/main/resources/hudson/cli/CliProtocol/description.jelly
core/src/main/resources/hudson/cli/CliProtocol2/description.jelly
core/src/main/resources/jenkins/slaves/JnlpSlaveAgentProtocol/description.jelly
core/src/main/resources/jenkins/slaves/JnlpSlaveAgentProtocol2/description.jelly
core/src/main/resources/jenkins/slaves/JnlpSlaveAgentProtocol3/description.jelly
core/src/main/resources/jenkins/slaves/JnlpSlaveAgentProtocol4/description.jelly

At a high level, I wanted to expose to the user, from a security
perspective, whether or not the protocols were secure and how.