Fix Gitea Valkey auth: inject password via env var interpolation

Valkey requires authentication. Use additionalConfigFromEnvs to
read the password from valkey-credentials secret and interpolate
it into the Redis URLs for cache and session config.

infra/kubernetes/platform/gitea/application.yaml

@@ -32,6 +32,15 @@ spec:
                 secretKeyRef:
                   name: gitea-pg-credentials
                   key: password
+            - name: VALKEY_PASSWORD
+              valueFrom:
+                secretKeyRef:
+                  name: valkey-credentials
+                  key: password
+            - name: GITEA__cache__HOST
+              value: redis://:$(VALKEY_PASSWORD)@valkey.platform.svc:6379/0
+            - name: GITEA__session__PROVIDER_CONFIG
+              value: redis://:$(VALKEY_PASSWORD)@valkey.platform.svc:6379/1
           config:
             database:
               DB_TYPE: postgres
@@ -40,10 +49,8 @@ spec:
               USER: gitea
             cache:
               ADAPTER: redis
-              HOST: redis://valkey.platform.svc:6379/0
             session:
               PROVIDER: redis
-              PROVIDER_CONFIG: redis://valkey.platform.svc:6379/1
             server:
               DOMAIN: gitea.coreworlds.io
               ROOT_URL: https://gitea.coreworlds.io