Add epoch_height config parameter

sequencer/api/migrations/V41__epoch_height.sql

@@ -0,0 +1,8 @@
+-- HotShotConfig was upgraded to include an `epoch_height` parameter. This migration initializes it
+-- with a default. We use the `||` operator to merge two JSON objects, one containing the default
+-- value for the new config parameter and one containing the existing config. When keys are present
+-- in both, the rightmost operand (the existing config) will take precedence.
+UPDATE network_config SET
+    config = jsonb_set(config, '{config}', '{
+        "epoch_height": 0
+    }' || (config->'config'));

sequencer/src/persistence/fs.rs

@@ -806,6 +806,12 @@ fn migrate_network_config(
         config.insert("stop_voting_time".into(), 0.into());
     }
 
+    // HotShotConfig was upgraded to include an `epoch_height` parameter. Initialize with a default
+    // if missing.
+    if !config.contains_key("epoch_height") {
+        config.insert("epoch_height".into(), 0.into());
+    }
+
     Ok(network_config)
 }