Add label field to task definition

Label is an alternative name for task that replace it when printed in following context eg.:

- log: when given task is up to date and is skipped from execution
- log: when given task is NOT up to date (`--status` command)
- in `--summary` and `--list` commands output

internal/summary/summary.go

@@ -56,7 +56,7 @@ func printTaskSummary(l *logger.Logger, t *taskfile.Task) {
 }
 
 func printTaskName(l *logger.Logger, t *taskfile.Task) {
-	l.Outf(logger.Default, "task: %s", t.Task)
+	l.Outf(logger.Default, "task: %s", t.Name())
 	l.Outf(logger.Default, "")
 }