feat: allow to change the config.toml file path

Now you can change the deafult location for the config file with an env
var:

```
TORRUST_IDX_BACK_CONFIG_PATH="./storage/config.toml" cargo run
```

The default location is still `./config.toml`

packages/configuration/src/lib.rs

@@ -512,10 +512,11 @@ impl Configuration {
         if Path::new(path).exists() {
             config = config_builder.add_source(File::with_name(path)).build()?;
         } else {
-            warn!("No config file found.");
-            warn!("Creating config file..");
+            warn!("No config file found. Creating config file ...");
+
             let config = Configuration::default();
             config.save_to_file(path)?;
+
             return Err(Error::CreatedNewConfigHalt {
                 location: Location::caller(),
                 path: path.to_string(),

src/bootstrap/config.rs

@@ -2,6 +2,7 @@
 //!
 //! All environment variables are prefixed with `TORRUST_TRACKER_BACK_`.
 use std::env;
+use std::path::Path;
 
 use torrust_tracker_configuration::Configuration;
 
@@ -11,6 +12,9 @@ use torrust_tracker_configuration::Configuration;
 /// Even if the file is not on the default path.
 const ENV_VAR_CONFIG: &str = "TORRUST_TRACKER_CONFIG";
 
+/// The `config.toml` file location.
+pub const ENV_VAR_CONFIG_PATH: &str = "TORRUST_IDX_BACK_CONFIG_PATH";
+
 // Default values
 
 const ENV_VAR_DEFAULT_CONFIG_PATH: &str = "./config.toml";
@@ -37,8 +41,14 @@ pub fn initialize_configuration() -> Configuration {
 
         Configuration::load_from_env_var(ENV_VAR_CONFIG).unwrap()
     } else {
-        println!("Loading configuration from config file {ENV_VAR_DEFAULT_CONFIG_PATH}");
+        let config_path = env::var(ENV_VAR_CONFIG_PATH).unwrap_or_else(|_| ENV_VAR_DEFAULT_CONFIG_PATH.to_string());
+
+        if Path::new(&config_path).is_file(){
+            println!("Loading configuration from config file: `{config_path}`");
+        } else {
+            println!("Creating default config file: `{config_path}`");
+        }
 
-        Configuration::load_from_file(ENV_VAR_DEFAULT_CONFIG_PATH).unwrap()
+        Configuration::load_from_file(&config_path).expect("Error loading configuration from file")
     }
 }