feat(upgrade): add --releasenotes: show release notes and skip upgrading

cli/internal/cli.go

@@ -95,6 +95,16 @@ var OfflineFlag = &cli.BoolFlag{
 	Usage:       "Prefer offline & filesystem access when possible",
 }
 
+// ReleaseNotes stores the variable from ReleaseNotesFlag.
+var ReleaseNotes bool
+
+// ReleaseNotesFlag turns on/off printing only release notes when upgrading.
+var ReleaseNotesFlag = &cli.BoolFlag{
+	Name:        "releasenotes, r",
+	Destination: &ReleaseNotes,
+	Usage:       "Only show release notes",
+}
+
 // MachineReadable stores the variable from MachineReadableFlag
 var MachineReadable bool