sqldb: fixup PostgreSQL fixture to allow creating separate DBs per test

This change will enable us to use a single PostgreSQL container instead of
spawning new a one for each (parallel) unit test reducing overall test
runtime.

sqldb/postgres_fixture.go

@@ -55,6 +55,7 @@ func NewTestPgFixture(t *testing.T, expiry time.Duration) *TestPgFixture {
 			"postgres",
 			"-c", "log_statement=all",
 			"-c", "log_destination=stderr",
+			"-c", "max_connections=1000",
 		},
 	}, func(config *docker.HostConfig) {
 		// Set AutoRemove to true so that stopped container goes away