feat: add support for Postgres database provider (#79)

backend/migrations/sqlite/20240924202721_user_groups.up.sql

@@ -0,0 +1,16 @@
+CREATE TABLE user_groups
+(
+    id           TEXT NOT NULL PRIMARY KEY,
+    created_at   DATETIME,
+    friendly_name TEXT NOT NULL,
+    name        TEXT NOT NULL UNIQUE
+);
+
+CREATE TABLE user_groups_users
+(
+    user_id  TEXT NOT NULL,
+    user_group_id TEXT NOT NULL,
+    PRIMARY KEY (user_id, user_group_id),
+    FOREIGN KEY (user_id) REFERENCES users (id) ON DELETE CASCADE,
+    FOREIGN KEY (user_group_id) REFERENCES user_groups (id) ON DELETE CASCADE
+);