perf-test: add memory test for notmuch-insert

In the future it might be worthwhile selecting corpus messages to
insert, but that seems a bit overcomplicated for now

performance-test/M06-insert.sh

@@ -0,0 +1,16 @@
+#!/bin/bash
+
+test_description='search'
+
+. ./perf-test-lib.sh || exit 1
+
+memory_start
+
+mkdir -p "$MAIL_DIR"/{cur,new,tmp}
+
+for count in {1..20}; do
+    generate_message "[file]=\"insert-$count\"" "[dir]='tmp/'"
+    memory_run "insert $count" "notmuch insert < $gen_msg_filename"
+done
+
+memory_done