feat(coderd/database): track user status changes over time (#16019)

RE: https://github.com/coder/coder/issues/15740,
https://github.com/coder/coder/issues/15297

In order to add a graph to the coder frontend to show user status over
time as an indicator of license usage, this PR adds the following:

* a new `api.insightsUserStatusCountsOverTime` endpoint to the API
* which calls a new `GetUserStatusCountsOverTime` query from postgres
* which relies on two new tables `user_status_changes` and
`user_deleted`
* which are populated by a new trigger and function that tracks updates
to the users table

The chart itself will be added in a subsequent PR

---------

Co-authored-by: Mathias Fredriksson <mafredri@gmail.com>

coderd/database/migrations/000283_user_status_changes.down.sql

@@ -0,0 +1,9 @@
+DROP TRIGGER IF EXISTS user_status_change_trigger ON users;
+
+DROP FUNCTION IF EXISTS record_user_status_change();
+
+DROP INDEX IF EXISTS idx_user_status_changes_changed_at;
+DROP INDEX IF EXISTS idx_user_deleted_deleted_at;
+
+DROP TABLE IF EXISTS user_status_changes;
+DROP TABLE IF EXISTS user_deleted;

coderd/database/migrations/000283_user_status_changes.up.sql

@@ -0,0 +1,75 @@
+CREATE TABLE user_status_changes (
+    id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+    user_id uuid NOT NULL REFERENCES users(id),
+    new_status user_status NOT NULL,
+    changed_at timestamptz NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+COMMENT ON TABLE user_status_changes IS 'Tracks the history of user status changes';
+
+CREATE INDEX idx_user_status_changes_changed_at ON user_status_changes(changed_at);
+
+INSERT INTO user_status_changes (
+    user_id,
+    new_status,
+    changed_at
+)
+SELECT
+    id,
+    status,
+    created_at
+FROM users
+WHERE NOT deleted;
+
+CREATE TABLE user_deleted (
+    id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+    user_id uuid NOT NULL REFERENCES users(id),
+    deleted_at timestamptz NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+COMMENT ON TABLE user_deleted IS 'Tracks when users were deleted';
+
+CREATE INDEX idx_user_deleted_deleted_at ON user_deleted(deleted_at);
+
+INSERT INTO user_deleted (
+	user_id,
+	deleted_at
+)
+SELECT
+	id,
+	updated_at
+FROM users
+WHERE deleted;
+
+CREATE OR REPLACE FUNCTION record_user_status_change() RETURNS trigger AS $$
+BEGIN
+    IF TG_OP = 'INSERT' OR OLD.status IS DISTINCT FROM NEW.status THEN
+        INSERT INTO user_status_changes (
+            user_id,
+            new_status,
+            changed_at
+        ) VALUES (
+            NEW.id,
+            NEW.status,
+            NEW.updated_at
+        );
+    END IF;
+
+    IF OLD.deleted = FALSE AND NEW.deleted = TRUE THEN
+        INSERT INTO user_deleted (
+            user_id,
+            deleted_at
+        ) VALUES (
+            NEW.id,
+            NEW.updated_at
+        );
+    END IF;
+
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER user_status_change_trigger
+    AFTER INSERT OR UPDATE ON users
+    FOR EACH ROW
+    EXECUTE FUNCTION record_user_status_change();

coderd/database/migrations/testdata/fixtures/000283_user_status_changes.up.sql

@@ -0,0 +1,42 @@
+INSERT INTO
+	users (
+		id,
+		email,
+		username,
+		hashed_password,
+		created_at,
+		updated_at,
+		status,
+		rbac_roles,
+		login_type,
+		avatar_url,
+		last_seen_at,
+		quiet_hours_schedule,
+		theme_preference,
+		name,
+		github_com_user_id,
+		hashed_one_time_passcode,
+		one_time_passcode_expires_at
+	)
+	VALUES (
+		'5755e622-fadd-44ca-98da-5df070491844', -- uuid
+		'test@example.com',
+		'testuser',
+		'hashed_password',
+		'2024-01-01 00:00:00',
+		'2024-01-01 00:00:00',
+		'active',
+		'{}',
+		'password',
+		'',
+		'2024-01-01 00:00:00',
+		'',
+		'',
+		'',
+		123,
+		NULL,
+		NULL
+	);
+
+UPDATE users SET status = 'dormant', updated_at = '2024-01-01 01:00:00' WHERE id = '5755e622-fadd-44ca-98da-5df070491844';
+UPDATE users SET deleted = true, updated_at = '2024-01-01 02:00:00' WHERE id = '5755e622-fadd-44ca-98da-5df070491844';