refactor: replace SSH fields in Environment with SshCredentials type

- Replace individual SSH fields (ssh_username, ssh_private_key_path, ssh_public_key_path) with single ssh_credentials field
- Update Environment constructor to accept SshCredentials instead of individual parameters
- Add ssh_credentials() accessor method for direct access to SSH credentials
- Update all SSH-related accessor methods to delegate to ssh_credentials fields
- Add required traits (Debug, Serialize, Deserialize) to SshCredentials struct
- Update all tests and documentation examples to use new constructor pattern
- Update E2E test binaries to use new SshCredentials pattern

This refactoring improves encapsulation by grouping SSH-related configuration
into a cohesive type that can be reused across the codebase.

Author: josecelano

src/bin/e2e_config_tests.rs

@@ -58,7 +58,7 @@ use torrust_tracker_deploy::e2e::tasks::{
     run_configuration_validation::run_configuration_validation,
 };
 use torrust_tracker_deploy::logging::{self, LogFormat};
-use torrust_tracker_deploy::shared::Username;
+use torrust_tracker_deploy::shared::{ssh::SshCredentials, Username};
 
 #[derive(Parser)]
 #[command(name = "e2e-config-tests")]
@@ -114,14 +114,14 @@ pub async fn main() -> Result<()> {
     let ssh_private_key_path = project_root.join("fixtures/testing_rsa");
     let ssh_public_key_path = project_root.join("fixtures/testing_rsa.pub");
     let ssh_user = Username::new("torrust").expect("Valid hardcoded username");
-
-    let environment = Environment::new(
-        env_name,
-        ssh_user.clone(),
+    let ssh_credentials = SshCredentials::new(
         ssh_private_key_path.clone(),
         ssh_public_key_path.clone(),
+        ssh_user.clone(),
     );
 
+    let environment = Environment::new(env_name, ssh_credentials);
+
     // Create and initialize TestContext
     let test_context =
         TestContext::from_environment(false, environment, TestContextType::Container)?.init()?;

src/bin/e2e_provision_tests.rs

@@ -50,7 +50,7 @@ use torrust_tracker_deploy::e2e::tasks::virtual_machine::{
     run_provision_command::run_provision_command,
 };
 use torrust_tracker_deploy::logging::{self, LogFormat};
-use torrust_tracker_deploy::shared::Username;
+use torrust_tracker_deploy::shared::{ssh::SshCredentials, Username};
 
 #[derive(Parser)]
 #[command(name = "e2e-provision-tests")]
@@ -115,14 +115,14 @@ pub async fn main() -> Result<()> {
     let ssh_private_key_path = project_root.join("fixtures/testing_rsa");
     let ssh_public_key_path = project_root.join("fixtures/testing_rsa.pub");
     let ssh_user = Username::new("torrust").expect("Valid hardcoded username");
-
-    let environment = Environment::new(
-        environment_name,
-        ssh_user.clone(),
+    let ssh_credentials = SshCredentials::new(
         ssh_private_key_path.clone(),
         ssh_public_key_path.clone(),
+        ssh_user.clone(),
     );
 
+    let environment = Environment::new(environment_name, ssh_credentials);
+
     let test_context =
         TestContext::from_environment(cli.keep, environment, TestContextType::VirtualMachine)?
             .init()?;

src/bin/e2e_tests_full.rs

@@ -63,7 +63,7 @@ use torrust_tracker_deploy::e2e::tasks::{
     },
 };
 use torrust_tracker_deploy::logging::{self, LogFormat};
-use torrust_tracker_deploy::shared::Username;
+use torrust_tracker_deploy::shared::{ssh::SshCredentials, Username};
 
 #[derive(Parser)]
 #[command(name = "e2e-tests")]
@@ -123,14 +123,14 @@ pub async fn main() -> Result<()> {
     let ssh_private_key_path = project_root.join("fixtures/testing_rsa");
     let ssh_public_key_path = project_root.join("fixtures/testing_rsa.pub");
     let ssh_user = Username::new("torrust").expect("Valid hardcoded username");
-
-    let environment = Environment::new(
-        environment_name,
-        ssh_user.clone(),
+    let ssh_credentials = SshCredentials::new(
         ssh_private_key_path.clone(),
         ssh_public_key_path.clone(),
+        ssh_user.clone(),
     );
 
+    let environment = Environment::new(environment_name, ssh_credentials);
+
     let test_context =
         TestContext::from_environment(cli.keep, environment, TestContextType::VirtualMachine)?
             .init()?;