Add way to specify database schema for extension-related helpers

[emmnull]

Some helpers are directly related to extensions installed by users. Such extensions are typically installed in their own schema. If users keep their database's or users' default search_path setting, this leads to having to prefix function calls or custom types with their host schema.

CREATE EXTENSION cube WITH SCHEMA extensions

-- Cube type or functions then generally need to be invoked using a pattern like "extensions"."cube"...

To circumvent this, we rely on forcing users to include their extensions schema to the search path. (see https://github.com/iolyd/drizzle-orm-helpers/blob/main/sql/search-path.sql). But we ideally want to let consumers decide how they manage their database settings, and we should thus provide a consistent way to include schemas with custom types and functions.

We could provide some type of instanciating functions à la

import {cube as _cube} from 'drizzle-orm-helpers/pg';

const extensionsSchema = pgSchema('extensions');
export const cube = createWithSchema(_cube, extensionsSchema)

But a good design should ideally not require devs to redeclare all functions within their code, maybe we could figure out some kind of global project config?