Update the initial event and span db tables

deployment/postgres-init-db/sql/tables/merlin/dataset/event.sql

@@ -6,6 +6,7 @@ create table merlin.event (
 
   value jsonb,
   topic_index integer not null,
+  span_index integer not null,
 
   constraint event_natural_key
     primary key (dataset_id, real_time, transaction_index, causal_time)

deployment/postgres-init-db/sql/tables/merlin/dataset/span.sql

@@ -8,9 +8,12 @@ create table merlin.span (
   duration interval null,
   type text not null,
   attributes jsonb not null,
+  span_index integer not null,
 
   constraint span_synthetic_key
-    primary key (dataset_id, id)
+    primary key (dataset_id, id),
+  constraint dataset_span_index_unique
+    unique (dataset_id, span_index)
 )
 partition by list (dataset_id);
 
@@ -32,6 +35,8 @@ comment on column merlin.span.type is e''
   'The type of span, implying the shape of its attributes.';
 comment on column merlin.span.attributes is e''
   'A set of named values annotating this span as a whole.';
+comment on column merlin.span.span_index is e''
+  'The true simulation span index';
 
 create function merlin.span_integrity_function()
   returns trigger