[SIMPL-30451] Add distributed-execution service with guide and reference implementations

Canonical location for documentation, example workflows and reference service implementations covering distributed execution patterns. Covers AC1-AC4: execution-target selection, decision support, readiness checks and code-level linkage. Tightly coupled jobs and the loosely coupled subprocess transport are verified by the test suite; the Kubernetes pipes transport is implemented but not yet cluster-run and is marked as such in the guide.

Changelog: added

yaml/values-dagster-distributed-execution.yaml

@@ -0,0 +1,54 @@
+dagster:
+  # ===========================================================================
+  # CODE LOCATION - distributed-execution
+  # ===========================================================================
+  # Deploys this repository as a Dagster code location so the reference jobs
+  # appear in the UI alongside production workflows.
+  # MANAGED BY GITLAB CI/CD - DO NOT CHANGE MANUALLY
+  dagster-user-deployments:
+    deployments:
+      - name: distributed-execution
+        location_name: distributed-execution
+        enabled: true
+        enableSubchart: true
+
+        codeServerArgs:
+          - "--host"
+          - "0.0.0.0"
+          - "--port"
+          - "4000"
+          - "--python-file"
+          - "src/distributed_execution/repository.py"
+
+        envFrom:
+          - secretRef:
+              name: distributed-execution-dagster-db-secret
+          - configMapRef:
+              name: distributed-execution-dagster-db-config
+
+        image:
+          pullPolicy: IfNotPresent
+          repository: code.europa.eu:4567/simpl/simpl-open/data/supporting-data-services/distributed-execution
+          tag: 0.0.0 # DO NOT CHANGE - replaced automatically by the pipeline before releasing
+
+        port: 4000
+
+        resources:
+          requests:
+            cpu: 100m
+            memory: 256Mi
+          limits:
+            cpu: 500m
+            memory: 512Mi
+
+        livenessProbe:
+          enabled: true
+          periodSeconds: 30
+          timeoutSeconds: 5
+          failureThreshold: 3
+
+        readinessProbe:
+          enabled: true
+          periodSeconds: 10
+          timeoutSeconds: 3
+          failureThreshold: 3