feat(dbtest): Mount DB dumps and create templates

Mount the benchmark dump directory when running
the test database and create a new script for creating
templates from the dumps. This makes it easy to create
pre-populated databases for benchmark tests.

Fixes https://hashicorp.atlassian.net/browse/ICU-4040

testing/dbtest/docker/Makefile

@@ -47,6 +47,7 @@ database-up:
 		-e PGDATA=/pgdata \
 		--mount type=tmpfs,destination=/pgdata \
 		-v "$(CWD)/../../../internal/db/schema/migrations":/migrations \
+		-v "$(CWD)/benchmark_dumps":/benchmark_dumps \
 		$(TEST_IMAGE_TAG) \
 		-c 'config_file=/etc/postgresql/postgresql.conf' \
 		$(PG_OPTS) 1> /dev/null