ReadySet Status: Add database connection status

Checks the connection to the upstream database and returns the status as
part of SHOW READYSET STATUS.

Release-Note-Core: Adds a status field for the connection between the
  ReadySet adapter and the upstream database to SHOW READYSET STATUS.
Change-Id: I989a0f7b49d01d130ab0586da90c0546f4a62b61
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/5713
Tested-by: Buildkite CI
Reviewed-by: Fran Noriega <fran@readyset.io>
Reviewed-by: Alex Martin <Alex.m@readyset.io>

readyset-adapter/src/backend.rs

@@ -1897,7 +1897,21 @@ where
                 self.show_caches(query_id).await
             }
             SqlQuery::Show(ShowStatement::ReadySetStatus) => {
-                self.noria.readyset_status(&self.authority).await
+                // Add upstream connectivity status
+                let additional_meta = if let Some(upstream) = &mut self.upstream {
+                    let connection_status = upstream
+                        .is_connected()
+                        .await
+                        .then(|| "Connected".to_string())
+                        .unwrap_or_else(|| "Unreachable".to_string());
+                    vec![("Database Connection".to_string(), connection_status)]
+                } else {
+                    vec![]
+                };
+
+                self.noria
+                    .readyset_status(&self.authority, additional_meta)
+                    .await
             }
             SqlQuery::Show(ShowStatement::ReadySetMigrationStatus(id)) => {
                 self.noria.migration_status(*id).await

readyset-adapter/src/backend/noria_connector.rs

@@ -940,9 +940,12 @@ impl NoriaConnector {
         Ok(QueryResult::Empty)
     }
 
+    /// Returns status provided by the Controller and persisted in the Authority. Also appends
+    /// additional_meta provided by the caller to the status.
     pub(crate) async fn readyset_status(
         &mut self,
         authority: &Authority,
+        mut additional_meta: Vec<(String, String)>,
     ) -> ReadySetResult<QueryResult<'static>> {
         let mut status =
             match noria_await!(self.inner.get_mut()?, self.inner.get_mut()?.noria.status()) {
@@ -977,7 +980,8 @@ impl NoriaConnector {
             ));
         }
 
-        // Converts from ReadySetStatus -> Vec<(String, String)> -> QueryResult
+        status.append(&mut additional_meta);
+
         Ok(QueryResult::MetaVariables(
             status.into_iter().map(MetaVariable::from).collect(),
         ))