fix(install): add migrate-pgbouncer.sh to install.sh (#4030)

Author: kodebach

install.sh

@@ -41,6 +41,7 @@ source install/bootstrap-snuba.sh
 source install/upgrade-postgres.sh
 source install/ensure-correct-permissions-profiles-dir.sh
 source install/set-up-and-migrate-database.sh
+source install/migrate-pgbouncer.sh
 source install/geoip.sh
 source install/setup-js-sdk-assets.sh
 source install/wrap-up.sh