Add support for RLS

[scribahti]

Enhancement.

It would be great to model RLS policies for Postgres with dbml and generate CREATE POLICY scripts with dbml2sql.

Suggested markup:

Policy {
  name 'Users can take all actions on their own accounts'
  schema public
  table users
  behavior permissive
  command all
  roles [authenticated]
  using `auth.uid() = user_id`
  check null
}

schema defaults to public if not provided.

behavior can have the values permissive or restrictive. It defaults to permissive if not provided.

command can have the values select, insert, update, delete, or all.

roles accepts a list of roles and defaults to public if none are provided.

using and check default to null if not provided.

[hdnax]

Hi @scribahti, thank you for your suggestion. I also saw that you've opened a PR (thanks for your contribution).

Regarding RLS, we're considering an approach listed in this discussion: #676.

Row-level security (RLS) primarily falls into the physical layer (also known as the physical data model and is more DBMS-specific compared to the existing DBML features.

We don't really want DBML to be too coupled to these details just yet. Instead, we want these as add-on metadata (like in the discussion above).

I think it would be nice if you could flesh out these ideas, as we're weighing many options regarding this issue.

[scribahti]

Replied in #676