op/doma/testnet: add Celestia Alt-DA support (celestiaorg/op-alt-da:v0.15.0)

- Add relay template (templates/relays/celestia.doma.yml) for op-alt-da
- Add celestia relay config to op/doma stack in context.yml
- Add relay: celestia to op/doma testnet in config.yml
- Add op-node.doma.yml template with ALTDA env vars gated on relay_name
- Update op/doma/testnet/rollup.json with complete config including alt_da block

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

compose_registry.json

@@ -6341,6 +6341,22 @@
       "boba-mainnet-op-reth-pruned-trace"
     ]
   },
+  {
+    "chain": "testnet",
+    "client": "reth",
+    "compose_file": "op/reth/doma-testnet-op-reth-pruned-trace",
+    "features": [
+      "trace"
+    ],
+    "network": "doma",
+    "node": "node",
+    "relay": "celestia",
+    "stack": "op",
+    "type": "pruned",
+    "volumes": [
+      "doma-testnet-op-reth-pruned-trace"
+    ]
+  },
   {
     "chain": "mainnet",
     "client": "reth",