add logging-otlp example (#790)

* Implement ToSchema for PhantomData<T>

* Add introduction of salvo-cli

* Optimization: take an uncommon name to avoid bugs with the same name as the user's

* Fix the code, pass the test

* Resolving Macro Expansion Errors

* add logging-otlp example

examples/logging-otlp/Cargo.toml

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+[package]
+name = "example-logging-otlp"
+version.workspace = true
+edition.workspace = true
+publish.workspace = true
+
+
+[dependencies]
+anyhow.workspace = true
+salvo = { workspace = true, features = ["logging"] }
+tokio = { workspace = true, features = ["macros"] }
+tracing.workspace = true
+tracing-subscriber ={ workspace = true, features = ["env-filter"] }
+tracing-opentelemetry = "0.23.0"
+opentelemetry = "0.22.0"
+opentelemetry-otlp = { version = "0.15.0", features = ["tonic"] }
+opentelemetry_sdk = { version = "0.22.1", features = ["rt-tokio"] }
+tracing-appender = "0.2.3"

examples/logging-otlp/README.md

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+# Salvo with OpenTelemetry OTLP Example
+
+## open-telemetry-otlp
+[otlp](https://opentelemetry.io/) High-quality, ubiquitous, and portable telemetry to enable effective observability
+
+This example demonstrates how to integrate the Salvo web framework with OpenTelemetry OTLP for tracing and logging, using Jaeger as the backend for visualization.
+
+## Prerequisites
+
+- Rust and Cargo installed on your system.
+- Docker installed for running Jaeger.
+
+## Running Jaeger with Docker
+
+Before running the application, you need to start Jaeger using Docker. This will set up Jaeger's UI and OTLP collector to receive telemetry data.
+
+```bash
+docker run -d -p 16686:16686 -p 4317:4317 -e COLLECTOR_OTLP_ENABLED=true jaegertracing/all-in-one:latest
+```
+
+
+## Running the Application
+Build and run the application:
+Access the example endpoint:
+```bash 
+curl http://localhost:5800/
+You should see "Hello World" as the response. Traces for requests made to this endpoint will be sent to Jaeger.
+```
+## Viewing Traces
+Open Jaeger UI in a web browser:
+http://localhost:16686
+Navigate to the Jaeger UI to view the traces and detailed telemetry data generated by interacting with the Salvo application.
+

examples/logging-otlp/src/main.rs

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+use anyhow::Result;
+use opentelemetry::KeyValue;
+use opentelemetry_otlp::WithExportConfig;
+use opentelemetry_sdk::{
+    runtime,
+    trace::{self, RandomIdGenerator, Tracer},
+    Resource,
+};
+use salvo::logging::Logger;
+use salvo::prelude::*;
+use tracing::{debug, info, instrument, level_filters::LevelFilter, warn};
+use tracing_subscriber::{
+    fmt::{self, format::FmtSpan},
+    layer::SubscriberExt,
+    util::SubscriberInitExt,
+    Layer,
+};
+
+#[instrument(fields(http.uri = req.uri().path(), http.method = req.method().as_str()))]
+#[handler]
+async fn hello(req: &mut Request) -> &'static str {
+    "Hello World"
+}
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    // console layer for tracing-subscriber
+    let console = fmt::Layer::new()
+        .with_span_events(FmtSpan::CLOSE)
+        .pretty()
+        .with_filter(LevelFilter::DEBUG);
+
+    // file appender layer for tracing-subscriber
+    let file_appender = tracing_appender::rolling::daily("./logs", "salvo.log");
+    let (non_blocking, _guard) = tracing_appender::non_blocking(file_appender);
+    let file = fmt::Layer::new()
+        .with_writer(non_blocking)
+        .pretty()
+        .with_filter(LevelFilter::INFO);
+
+    // opentelemetry tracing layer for tracing-subscriber
+    let tracer = init_tracer()?;
+    let opentelemetry = tracing_opentelemetry::layer().with_tracer(tracer);
+
+    tracing_subscriber::registry()
+        .with(console)
+        .with(file)
+        .with(opentelemetry)
+        .init();
+
+    let router = Router::new().get(hello);
+    let service = Service::new(router).hoop(Logger::new());
+
+    let acceptor = TcpListener::new("0.0.0.0:5800").bind().await;
+    Server::new(acceptor).serve(service).await;
+    Ok(())
+}
+
+fn init_tracer() -> anyhow::Result<Tracer> {
+    let tracer = opentelemetry_otlp::new_pipeline()
+        .tracing()
+        .with_exporter(
+            opentelemetry_otlp::new_exporter()
+                .tonic()
+                .with_endpoint("http://localhost:4317"),
+        )
+        .with_trace_config(
+            trace::config()
+                .with_id_generator(RandomIdGenerator::default())
+                .with_max_events_per_span(32)
+                .with_max_attributes_per_span(64)
+                .with_resource(Resource::new(vec![KeyValue::new("service.name", "salvo-tracing")])),
+        )
+        .install_batch(runtime::Tokio)?;
+    Ok(tracer)
+}