refactor: extract Docker Image Builder with constants

- Extract DockerImageBuilder as independent module with builder pattern
- Implement required field validation and comprehensive error handling
- Add DEFAULT_IMAGE_NAME and DEFAULT_IMAGE_TAG constants to eliminate duplication
- Provide fluent interface with method chaining for configuration
- Maintain backward compatibility with existing provisioned container API
- Add 13 unit tests for builder validation and error scenarios

Implements point 1 of provisioned container refactoring plan

Author: josecelano

docs/refactors/provisioned-container-refactoring.md

@@ -65,36 +65,58 @@ This structure enables:
 
 ## 🏗️ Architecture & Design Patterns
 
-### 1. Extract Docker Image Builder
+### ✅ 1. Extract Docker Image Builder (Completed)
 
-**Current Issue**: Docker image building logic is embedded in the container state machine.
+**Issue Resolved**: Docker image building logic was embedded in the container state machine.
 
-**Proposed Solution**:
+**Implementation Completed**:
 
 ```rust
 pub struct DockerImageBuilder {
-    image_name: String,
-    tag: String,
-    dockerfile_path: PathBuf,
-    context_path: PathBuf,
-    build_timeout: Duration,
+    image_name: Option<String>,        // Required field validation
+    tag: String,                       // Default: "latest"
+    dockerfile_path: Option<PathBuf>,  // Required field validation
+    context_path: PathBuf,             // Default: "."
+    build_timeout: Duration,           // Default: 300 seconds
 }
 
 impl DockerImageBuilder {
     pub fn new() -> Self { /* ... */ }
     pub fn with_name(mut self, name: impl Into<String>) -> Self { /* ... */ }
     pub fn with_tag(mut self, tag: impl Into<String>) -> Self { /* ... */ }
     pub fn with_dockerfile(mut self, path: PathBuf) -> Self { /* ... */ }
+    pub fn with_context(mut self, path: PathBuf) -> Self { /* ... */ }
+    pub fn with_build_timeout(mut self, timeout: Duration) -> Self { /* ... */ }
     pub fn build(&self) -> Result<()> { /* ... */ }
+    pub fn image_tag(&self) -> String { /* ... */ }
+}
+
+// Comprehensive error handling
+#[derive(Debug, thiserror::Error)]
+pub enum DockerBuildError {
+    #[error("Failed to execute docker build command for image '{image_name}:{tag}': {source}")]
+    DockerBuildExecution { /* ... */ },
+    #[error("Docker build failed for image '{image_name}:{tag}' with stderr: {stderr}")]
+    DockerBuildFailed { /* ... */ },
+    #[error("Image name is required but was not provided")]
+    ImageNameRequired,
+    #[error("Dockerfile path is required but was not provided")]
+    DockerfilePathRequired,
 }
 ```
 
-**Benefits**:
+**Benefits Achieved**:
+
+- ✅ Single Responsibility Principle
+- ✅ Explicit configuration with required field validation
+- ✅ Comprehensive error handling with specific error types
+- ✅ Builder pattern with method chaining
+- ✅ Full test coverage (13 unit tests)
+- ✅ Integration with existing provisioned container error chain
+- ✅ Reusable across different container types
+- ✅ Configurable image parameters with sensible defaults
 
-- Single Responsibility Principle
-- Easier testing of build logic
-- Configurable image parameters
-- Reusable across different container types
+**Module Location**: `src/e2e/containers/docker_builder.rs`
 
 ### 2. Container Configuration Builder
 
@@ -513,9 +535,9 @@ let container = StoppedProvisionedContainer::builder()
 3. ✅ **Documentation Updates** - Updated all references to new module structure
 4. ✅ **Test Validation** - Ensured all tests pass with new structure
 
-### Phase 1: Foundation (High Priority)
+### ✅ Phase 1: Foundation (High Priority) - Partially Complete
 
-1. Extract Docker Image Builder
+1. ✅ **Extract Docker Image Builder** - Implemented independent `DockerImageBuilder` with builder pattern, explicit configuration, required field validation, comprehensive error handling, and full integration with provisioned container module
 2. Improve Error Context
 3. Extract Magic Numbers and Strings
 4. Split Large Functions

src/bin/e2e_config_tests.rs

@@ -33,8 +33,8 @@ use tracing::{error, info};
 use torrust_tracker_deploy::application::commands::ConfigureCommand;
 use torrust_tracker_deploy::config::{Config, InstanceName, SshCredentials};
 use torrust_tracker_deploy::container::Services;
-use torrust_tracker_deploy::e2e::environment::TestEnvironment;
 use torrust_tracker_deploy::e2e::containers::StoppedProvisionedContainer;
+use torrust_tracker_deploy::e2e::environment::TestEnvironment;
 use torrust_tracker_deploy::e2e::tasks::preflight_cleanup;
 use torrust_tracker_deploy::e2e::tasks::provision_docker_infrastructure::provision_docker_infrastructure;
 use torrust_tracker_deploy::logging::{self, LogFormat};