fix: Use the right name for PostHook (#2599)

There is no such type of hook as AfterHook used in the Plan resource.
hook_type='AfterHook' is not a valid Forklift API value and never was
(only PreHook and PostHook are valid). Any code using after_hook_name
would fail with HookStepNotValid error.
The correct type is PostHook.

Co-authored-by: Meni Yakove <441263+myakove@users.noreply.github.com>

Author: krcmarik

ocp_resources/plan.py

@@ -120,7 +120,7 @@ def __init__(
                 self._generate_hook_spec(
                     hook_name=self.after_hook_name,
                     hook_namespace=self.after_hook_namespace,
-                    hook_type="AfterHook",
+                    hook_type="PostHook",
                 )
             )