fix(dex): 🔐 correct sizer client secret to match sizer-oidc-client

The deploy hydration created dex-sizer-client with wrong value.
Reverting to the original shared secret that sizer expects
(73eda906... - active for 81 days before hydration overwrote it).

Changes:
- sizer-oidc-client: restore correct shared secret
- dex-sizer-client: add managed manifest to prevent future drift
- dex.yaml: add manifests source for ArgoCD to sync the secret

Broken by stacks rehydration pipeline run.

otc/dev.t09.de/stacks/ci-sizer/sizer-receiver/secret.yaml

@@ -6,4 +6,4 @@ metadata:
     app: sizer-receiver
 type: Opaque
 stringData:
-  client-secret: "di4ul3ce6D796q19lVQsjiGBVzluC/J7WCzjNDRZKKMRr/+C"
+  client-secret: "73eda9068bd00dfe67d29f087b5540cb1cd82cc1dd2ac0f838558ac8bbcfcb3a"

otc/dev.t09.de/stacks/core/dex.yaml

@@ -27,3 +27,6 @@ spec:
     - repoURL: https://edp.buildth.ing/DevFW-CICD/stacks-instances
       targetRevision: HEAD
       ref: values
+    - repoURL: https://edp.buildth.ing/DevFW-CICD/stacks-instances
+      targetRevision: HEAD
+      path: "otc/dev.t09.de/stacks/core/dex/manifests"

otc/dev.t09.de/stacks/core/dex/manifests/dex-sizer-client.yaml

@@ -0,0 +1,8 @@
+apiVersion: v1
+kind: Secret
+metadata:
+  name: dex-sizer-client
+  namespace: dex
+type: Opaque
+stringData:
+  clientSecret: "73eda9068bd00dfe67d29f087b5540cb1cd82cc1dd2ac0f838558ac8bbcfcb3a"