1. only implement post-renderer flags this patch
2. As mumoshu advise, add helmfile flags `--post-render` and add the
postRenderer config in helmDefaults and release. the priority is
helmfile flags > release > helmDefaults.
3. fix the test case in state_test.go and some other tests.
Signed-off-by: guofutan <guofutan@tencent.com>
Signed-off-by: yxxhero <aiopsclub@163.com>