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/queries/providers.rs

@@ -0,0 +1,67 @@
+use sea_orm::sea_query::OnConflict;
+use sea_orm::QueryOrder;
+
+use super::*;
+
+impl LlmDatabase {
+    pub async fn initialize_providers(&self) -> Result<()> {
+        self.transaction(|tx| async move {
+            let providers_and_models = vec![
+                ("anthropic", "claude-3-5-sonnet"),
+                ("anthropic", "claude-3-opus"),
+                ("anthropic", "claude-3-sonnet"),
+                ("anthropic", "claude-3-haiku"),
+            ];
+
+            for (provider_name, model_name) in providers_and_models {
+                let insert_provider = provider::Entity::insert(provider::ActiveModel {
+                    name: ActiveValue::set(provider_name.to_owned()),
+                    ..Default::default()
+                })
+                .on_conflict(
+                    OnConflict::columns([provider::Column::Name])
+                        .update_column(provider::Column::Name)
+                        .to_owned(),
+                );
+
+                let provider = if tx.support_returning() {
+                    insert_provider.exec_with_returning(&*tx).await?
+                } else {
+                    insert_provider.exec_without_returning(&*tx).await?;
+                    provider::Entity::find()
+                        .filter(provider::Column::Name.eq(provider_name))
+                        .one(&*tx)
+                        .await?
+                        .ok_or_else(|| anyhow!("failed to insert provider"))?
+                };
+
+                model::Entity::insert(model::ActiveModel {
+                    provider_id: ActiveValue::set(provider.id),
+                    name: ActiveValue::set(model_name.to_owned()),
+                    ..Default::default()
+                })
+                .on_conflict(
+                    OnConflict::columns([model::Column::ProviderId, model::Column::Name])
+                        .update_column(model::Column::Name)
+                        .to_owned(),
+                )
+                .exec_without_returning(&*tx)
+                .await?;
+            }
+
+            Ok(())
+        })
+        .await
+    }
+
+    /// Returns the list of LLM providers.
+    pub async fn list_providers(&self) -> Result<Vec<provider::Model>> {
+        self.transaction(|tx| async move {
+            Ok(provider::Entity::find()
+                .order_by_asc(provider::Column::Name)
+                .all(&*tx)
+                .await?)
+        })
+        .await
+    }
+}