Add index for interactive search (#493)

atuin-client/migrations/20220806155627_interactive_search_index.sql

@@ -0,0 +1,6 @@
+-- Interactive search filters by command then by the max(timestamp) for that
+-- command. Create an index that covers those
+create index if not exists idx_history_command_timestamp on history(
+	command,
+	timestamp
+);