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

examples/postgres/users-comments-and-followers/src/cli/mod.rs

@@ -0,0 +1,40 @@
+use clap::{Parser, Subcommand};
+
+mod comments;
+mod followers;
+mod users;
+
+type Result = crate::Result<()>;
+
+pub trait Executable {
+    async fn execute(&self, pool: &sqlx::PgPool) -> Result;
+}
+
+#[derive(Debug, Clone, Parser)]
+pub struct Cli {
+    #[command(subcommand)]
+    pub command: Commands,
+}
+
+impl Executable for Cli {
+    async fn execute(&self, pool: &sqlx::PgPool) -> Result {
+        self.command.execute(pool).await
+    }
+}
+
+#[derive(Debug, Clone, Subcommand)]
+pub enum Commands {
+    Users(users::UserArgs),
+    Followers(followers::FollowersArgs),
+    Comments(comments::CommentArgs),
+}
+
+impl Executable for Commands {
+    async fn execute(&self, pool: &sqlx::PgPool) -> Result {
+        match self {
+            Commands::Users(user_args) => user_args.execute(pool).await,
+            Commands::Followers(followers_args) => followers_args.execute(pool).await,
+            Commands::Comments(comment_args) => comment_args.execute(pool).await,
+        }
+    }
+}