UI: update OIDC image alt text to be more informative (#31083)

* update alt text to be more informative

* update alt text

Author: lane-wetmore

ui/app/templates/vault/cluster/access/oidc/index.hbs

@@ -15,5 +15,9 @@
 </div>
 
 <div class="box is-fullwidth is-shadowless">
-  <img data-test-oidc-img src={{img-path "~/oidc-landing.png"}} alt="OIDC configure diagram" />
+  <img
+    data-test-oidc-img
+    src={{img-path "~/oidc-landing.png"}}
+    alt="Example flow of a user logging in to an application, which redirects them to the Vault U-I for authentication. Vault displays an auth method selection form and forwards the user to an upstream identity provider (like A-W-S, Okta, or Microsoft) for final credential verification."
+  />
 </div>