collab: Setup database for LLM service (#15882)

This PR puts the initial infrastructure for the LLM service's database
in place.

The LLM service will be using a separate Postgres database, with its own
set of migrations.

Currently we only connect to the database in development, as we don't
yet have the database setup for the staging/production environments.

Release Notes:

- N/A

crates/collab/src/llm/db/ids.rs

@@ -0,0 +1,7 @@
+use sea_orm::{entity::prelude::*, DbErr};
+use serde::{Deserialize, Serialize};
+
+use crate::id_type;
+
+id_type!(ProviderId);
+id_type!(ModelId);