change authn blog date to 2024-04-25 and add intro

Signed-off-by: Anish Ramasekar <[email protected]>

Author: aramase

content/en/blog/_posts/2024-04-29-structured-authentication-configuration-beta.md renamed to content/en/blog/_posts/2024-04-25-structured-authentication-configuration-beta.md

@@ -1,14 +1,18 @@
 ---
 layout: blog
 title: "Kubernetes 1.30: Structured Authentication Configuration Moves to Beta"
-date: 2024-04-29
+date: 2024-04-25
 slug: structured-authentication-moves-to-beta
 ---
 
 **Author:** [Anish Ramasekar](https://github.com/aramase) (Microsoft)
 
 With Kubernetes 1.30, we (SIG Auth) are moving Structured Authentication Configuration to beta.
 
+Today's article is about _authentication_: finding out who's performing a task, and checking
+that they are who they say they are. Check back in tomorrow to find about what's new in
+Kubernetes v1.30 around _authorization_ (deciding what someone can and can't access).
+
 ## Motivation
 Kubernetes has had a long-standing need for a more flexible and extensible
 authentication system. The current system, while powerful, has some limitations