Add linux-{buildinfo,image-unsigned,source} versioned kernel pkgs

LP: #1821640

debian/apt.conf.autoremove

@@ -17,6 +17,7 @@ APT
 	"linux-modules";
 	"linux-modules-extra";
 	"linux-signed-image";
+	"linux-image-unsigned";
 	# kfreebsd kernels
 	"kfreebsd-image";
 	"kfreebsd-headers";
@@ -30,6 +31,10 @@ APT
         # tools
         "linux-tools";
         "linux-cloud-tools";
+	# build info
+	"linux-buildinfo";
+	# source code
+	"linux-source";
   };
 
   Never-MarkAuto-Sections