adapter: Thread for_cache to controller graphviz request

Thread the contents of the FOR CACHE clause, if present, all the way
through to the graphviz controller RPC. This allows running EXPLAIN
[SIMPLIFIED] GRAPHVIZ [FOR CACHE <q>] in a SQL console.

Release-Note-Core: Add a new `FOR CACHE <q>` clause to the end of the
  `EXPLAIN GRAPHVIZ` SQL command to allow limiting the generated
  graphviz to only the nodes for a named cached query.
Change-Id: I2cf07903a51f992e0b3fd27170c599ae9bde324e
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/6131
Tested-by: Buildkite CI
Reviewed-by: Luke Osborne <luke@readyset.io>

readyset-adapter/src/backend.rs

@@ -1914,9 +1914,10 @@ where
             SqlQuery::Explain(nom_sql::ExplainStatement::LastStatement) => {
                 self.explain_last_statement()
             }
-            SqlQuery::Explain(nom_sql::ExplainStatement::Graphviz { simplified, .. }) => {
-                self.noria.graphviz(*simplified).await
-            }
+            SqlQuery::Explain(nom_sql::ExplainStatement::Graphviz {
+                simplified,
+                for_cache,
+            }) => self.noria.graphviz(*simplified, for_cache.clone()).await,
             SqlQuery::Explain(nom_sql::ExplainStatement::Domains) => {
                 self.noria.explain_domains().await
             }

readyset-adapter/src/backend/noria_connector.rs

@@ -523,6 +523,7 @@ impl NoriaConnector {
     pub(crate) async fn graphviz(
         &mut self,
         simplified: bool,
+        for_query: Option<Relation>,
     ) -> ReadySetResult<QueryResult<'static>> {
         let label = if simplified {
             "SIMPLIFIED GRAPHVIZ"
@@ -536,7 +537,7 @@ impl NoriaConnector {
             .noria
             .graphviz(GraphvizOptions {
                 detailed: !simplified,
-                ..Default::default()
+                for_query,
             })
             .await?;