feat(examples): add PostgreSQL example with user relationship

Adds an example demonstrating user, comment, and follower relationship
including:
- User management with profiles
- Comments (not really useful, just for showcasing)
- Follower/follozing relationships
- Ineractive CLI interface with CRUD operations
- Database migrations for the example schema

Cargo.toml

@@ -1,5 +1,9 @@
 [workspace]
-members = [".", "georm-macros"]
+members = [
+    ".",
+    "georm-macros",
+    "examples/postgres/*"
+]
 
 [workspace.package]
 version = "0.1.1"