This function retrieves all jobs existing on this jenkins instance and
group them by "assigned label", keeping only such labels that contains
the particular label of this LabelLinkedJobsAction instance
JENKINS-25188 - Orphaned jobs do not show jobs without label when all nodes set to Label restrictions
This function scans all nodes to determine if at least one is in non-exclusive mode,
meaning it can be used to run jobs with no labels.
One ExtensionPoint of this plugin
adds an Action, which makes an additional link available for Labels in the left-hand side menu to see linked jobs
defines the Descriptor class, which manages the plugin configuration per label - that is,
returns the name of the option to activate the plugin for that label
See LabelConfigurationDescriptor.getDisplayName()
This constructor is called by jenkins when the user saves
the configuration page of a given label, and has selected
the checkbox to activate this extension.