feat!: rename supported kernels to targets

BREAKING CHANGE: .out-of-tree.toml: s/[[supported_kernels]]/[[targets]]/

kernel.go

@@ -107,7 +107,7 @@ func (cmd KernelAutogenCmd) Run(kernelCmd *KernelCmd, g *Globals) (err error) {
 	shutdown := false
 	kernel.SetSigintHandler(&shutdown)
 
-	for _, sk := range ka.SupportedKernels {
+	for _, sk := range ka.Targets {
 		if sk.Distro.Release == "" {
 			err = errors.New("Please set distro_release")
 			return