Add migration for data sources. (#5008)

This migration adds support for three additional tables,
`data_sources` and `data_sources_functions` containing the definition
of a single data source in a many-to-one relationship, and a
`rule_type_data_sources` table representing the many-to-many
relationship between rule types and data sources.

Author: blkt

database/migrations/000108_data_sources.down.sql

@@ -0,0 +1,10 @@
+-- SPDX-FileCopyrightText: Copyright 2024 The Minder Authors
+-- SPDX-License-Identifier: Apache-2.0
+
+BEGIN;
+
+DROP TABLE rule_type_data_sources;
+DROP TABLE data_sources_functions;
+DROP TABLE data_sources;
+
+COMMIT;

database/migrations/000108_data_sources.up.sql

@@ -0,0 +1,60 @@
+-- SPDX-FileCopyrightText: Copyright 2024 The Minder Authors
+-- SPDX-License-Identifier: Apache-2.0
+
+BEGIN;
+
+-- This migration adds storage support for data sources. The only
+-- constraints we enforce at the database layer are
+--
+-- * functions can only reference one data source, and must be deleted
+--   if the data source is deleted
+-- * data sources are tied to a project, and must be deleted if the
+--   project is deleted
+-- * rule types can reference one or more data source, and we want to
+--   prevent deletion of a data source if there's a rule type
+--   referencing it
+--
+-- The first two are simple foreign keys, while the third one is
+-- enforced by the lack of `ON DELETE ...` clause in the
+-- `rule_type_data_sources` table.
+--
+-- We also want to prevent the creation of a data source with a given
+-- name if another data source with the same name exists in the
+-- project hierarchy. I'm not sure how to express this as a database
+-- constraint, nor I believe this would be efficient, so we decided to
+-- let the application layer enforce that as we do with profiles.
+
+CREATE TABLE data_sources(
+    id UUID NOT NULL DEFAULT gen_random_uuid() PRIMARY KEY,
+    name TEXT NOT NULL,
+    display_name TEXT NOT NULL,
+    project_id UUID NOT NULL,
+    created_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT NOW(),
+    FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE
+);
+
+CREATE UNIQUE INDEX data_sources_name_lower_idx ON data_sources (project_id, lower(name));
+
+CREATE TABLE data_sources_functions(
+    id UUID NOT NULL DEFAULT gen_random_uuid() PRIMARY KEY,
+    name TEXT NOT NULL,
+    type TEXT NOT NULL,
+    data_source_id UUID NOT NULL,
+    definition JSONB NOT NULL,
+    created_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT NOW(),
+    FOREIGN KEY (data_source_id) REFERENCES data_sources(id) ON DELETE CASCADE
+);
+
+CREATE UNIQUE INDEX data_sources_functions_name_lower_idx ON data_sources_functions (data_source_id, lower(name));
+
+CREATE TABLE rule_type_data_sources(
+    rule_type_id UUID NOT NULL,
+    data_sources_id UUID NOT NULL,
+    FOREIGN KEY (rule_type_id) REFERENCES rule_type(id),
+    FOREIGN KEY (data_sources_id) REFERENCES data_sources(id),
+    UNIQUE (rule_type_id, data_sources_id)
+);
+
+COMMIT;