feat: [#656] Tracker Checker sopports env var for config

Run providing a config file path:

```text
cargo run --bin tracker_checker -- --config-path "./share/default/config/tracker_checker.json"
TORRUST_CHECKER_CONFIG_PATH="./share/default/config/tracker_checker.json" cargo run --bin tracker_checker
```

Run providing the configuration:

```text
TORRUST_CHECKER_CONFIG=$(cat "./share/default/config/tracker_checker.json") cargo run --bin tracker_checker
```

src/bin/tracker_checker.rs

@@ -1,7 +1,16 @@
 //! Program to run checks against running trackers.
 //!
+//! Run providing a config file path:
+//!
+//! ```text
+//! cargo run --bin tracker_checker -- --config-path "./share/default/config/tracker_checker.json"
+//! TORRUST_CHECKER_CONFIG_PATH="./share/default/config/tracker_checker.json" cargo run --bin tracker_checker
+//! ```
+//!
+//! Run providing the configuration:
+//!
 //! ```text
-//! cargo run --bin tracker_checker "./share/default/config/tracker_checker.json"
+//! TORRUST_CHECKER_CONFIG=$(cat "./share/default/config/tracker_checker.json") cargo run --bin tracker_checker
 //! ```
 use torrust_tracker::checker::app;
 

src/checker/app.rs

@@ -1,7 +1,7 @@
 use std::path::PathBuf;
 use std::sync::Arc;
 
-use anyhow::Context;
+use anyhow::{Context, Result};
 use clap::Parser;
 
 use super::config::Configuration;
@@ -12,16 +12,22 @@ use crate::checker::config::parse_from_json;
 #[derive(Parser, Debug)]
 #[clap(author, version, about, long_about = None)]
 struct Args {
-    config_path: PathBuf,
+    /// Path to the JSON configuration file.
+    #[clap(short, long, env = "TORRUST_CHECKER_CONFIG_PATH")]
+    config_path: Option<PathBuf>,
+
+    /// Direct configuration content in JSON.
+    #[clap(env = "TORRUST_CHECKER_CONFIG", hide_env_values = true)]
+    config_content: Option<String>,
 }
 
 /// # Errors
 ///
-/// Will return an error if it can't read or parse the configuration file.
-pub async fn run() -> anyhow::Result<Vec<CheckResult>> {
+/// Will return an error if the configuration was not provided.
+pub async fn run() -> Result<Vec<CheckResult>> {
     let args = Args::parse();
 
-    let config = setup_config(&args)?;
+    let config = setup_config(args)?;
 
     let console_printer = Console {};
 
@@ -33,9 +39,16 @@ pub async fn run() -> anyhow::Result<Vec<CheckResult>> {
     Ok(service.run_checks().await)
 }
 
-fn setup_config(args: &Args) -> anyhow::Result<Configuration> {
-    let file_content =
-        std::fs::read_to_string(&args.config_path).with_context(|| format!("can't read config file {:?}", args.config_path))?;
+fn setup_config(args: Args) -> Result<Configuration> {
+    match (args.config_path, args.config_content) {
+        (Some(config_path), _) => load_config_from_file(&config_path),
+        (_, Some(config_content)) => parse_from_json(&config_content).context("invalid config format"),
+        _ => Err(anyhow::anyhow!("no configuration provided")),
+    }
+}
+
+fn load_config_from_file(path: &PathBuf) -> Result<Configuration> {
+    let file_content = std::fs::read_to_string(path).with_context(|| format!("can't read config file {path:?}"))?;
 
     parse_from_json(&file_content).context("invalid config format")
 }

src/e2e/runner.rs

@@ -197,14 +197,14 @@ fn write_tracker_checker_config_file(config_file_path: &Path, config: &str) {
 /// Will panic if the config path is not a valid string.
 pub fn run_tracker_checker(config_path: &Path) -> io::Result<()> {
     info!(
-        "Running Tracker Checker: cargo --bin tracker_checker {}",
+        "Running Tracker Checker: cargo run --bin tracker_checker -- --config-path \"{}\"",
         config_path.display()
     );
 
     let path = config_path.to_str().expect("The path should be a valid string");
 
     let status = Command::new("cargo")
-        .args(["run", "--bin", "tracker_checker", path])
+        .args(["run", "--bin", "tracker_checker", "--", "--config-path", path])
         .status()?;
 
     if status.success() {