refactor(preview-service): conforms to design patterns, adds tests, and is typed (#2429)

Co-authored-by: Kristaps Fabians Geikins <fabis94@live.com>

setup/db/10-docker_postgres_init.sql

@@ -1,8 +1,20 @@
 CREATE DATABASE speckle2_test
-    WITH 
+    WITH
     OWNER = speckle
     ENCODING = 'UTF8'
     LC_COLLATE = 'en_US.utf8'
     LC_CTYPE = 'en_US.utf8'
     TABLESPACE = pg_default
-    CONNECTION LIMIT = -1;
+    CONNECTION LIMIT = -1;
+CREATE USER preview_service_test WITH PASSWORD 'preview_service_test';
+CREATE DATABASE preview_service_test
+    WITH
+    OWNER = preview_service_test
+    ENCODING = 'UTF8'
+    LC_COLLATE = 'en_US.utf8'
+    LC_CTYPE = 'en_US.utf8'
+    TABLESPACE = pg_default
+    CONNECTION LIMIT = -1;
+GRANT CREATE ON TABLESPACE pg_default TO preview_service_test; -- required to create databases
+ALTER USER preview_service_test CREATEDB; -- Allow user to create databases
+GRANT pg_write_all_data TO preview_service_test;