migration --from-server should take --exclude-schema argument

When using `hasura migrate create "name" --from-server`, the migration does not contain the Postgres extensions. This will fail when used on a fresh database instance.

### Example
We're using a multi-database single-tenant setup, which means we have an Hasura instance for each database, and every database belongs to a single, specific tenant. All databases are structured the same way.

When creating the first migration from an existing database, the migration will not contain the `uuid-ossp`, and thus fails when applied to a fresh instance.

### Steps to reproduce
- **Setup**
- Postgres
- Create a new database
- Add the `uuid-ossp` extension
- Set up a table using that extension (e.g column `id uuid DEFAULT public.uuid_generate_v4() NOT
NULL`)
- Hasura
- Run a fresh instance and connect to the database
- `hasura init --directory my-project --endpoint http://localhost:8080`
- `cd my-project`
- `hasura migrate create "init" --from-server`
- **Reproduce**
- Drop the database and close the Hasura instance
- Create a new database and open a new Hasura instance
- Apply the migration: `hasura migrate apply --version ""`

This will fail (you can examine the generated up.sql. It does not contain the extension).