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/Dockerfile.12-alpine

@@ -1,6 +1,7 @@
 FROM postgres:12-alpine
 
 ADD init-db.sh /docker-entrypoint-initdb.d/00-init-db.sh
+ADD restore-benchmark-dumps.sh /docker-entrypoint-initdb.d/01-restore-benchmark-dumps.sh
 ADD postgresql.conf /etc/postgresql/postgresql.conf
 
 CMD ["postgres", "-c", "config_file=/etc/postgresql/postgresql.conf"]