feat: [#208] Add provider configuration to EnvironmentCreationConfig

[josecelano]

Summary

This PR implements issue #208 from the Hetzner Provider Support epic (#205).

Changes

Core Configuration Updates

• Add provider field to EnvironmentCreationConfig (uses ProviderSection for JSON parsing)
• Add instance_name optional field to EnvironmentSection (auto-generated as torrust-tracker-vm-{env_name} if not provided)
• Update to_environment_params() to return (EnvironmentName, InstanceName, ProviderConfig, SshCredentials, port)

Error Handling

• Add InvalidInstanceName error variant with actionable help message

CLI Updates

• Add clap::ValueEnum derive to Provider enum for CLI argument parsing
• Add --provider/-p required argument to create template command
• Generate provider-specific templates:
  • LXD: Includes profile_name placeholder
  • Hetzner: Includes api_token, server_type, location placeholders

Documentation

• Update docs/user-guide/commands/create.md with new configuration format
• Update help messages to show both LXD and Hetzner template generation commands

Tests

• Update all tests to include provider configuration in JSON fixtures

Breaking Changes

⚠️ Environment JSON files now require a provider section

⚠️ create template command now requires --provider argument

Example Configurations

LXD Provider

{
  "environment": {
    "name": "dev",
    "instance_name": "torrust-tracker-vm-dev"
  },
  "ssh_credentials": {
    "private_key_path": "fixtures/testing_rsa",
    "public_key_path": "fixtures/testing_rsa.pub",
    "username": "torrust",
    "port": 22
  },
  "provider": {
    "provider": "lxd",
    "profile_name": "torrust-profile-dev"
  }
}

Hetzner Provider

{
  "environment": {
    "name": "prod",
    "instance_name": "torrust-tracker-demo"
  },
  "ssh_credentials": {
    "private_key_path": "~/.ssh/id_rsa",
    "public_key_path": "~/.ssh/id_rsa.pub",
    "username": "torrust",
    "port": 22
  },
  "provider": {
    "provider": "hetzner",
    "api_token": "your-hetzner-api-token",
    "server_type": "cx22",
    "location": "nbg1"
  }
}

Testing

• All 1228 library tests pass
• All 300 doc tests pass
• E2E provision and destroy tests pass
• E2E configuration tests pass
• E2E full test passes
• Pre-commit checks pass

Related Issues

• Closes Update EnvironmentCreationConfig DTO #208
• Part of Epic Epic: Add Hetzner Provider Support #205 (Add Hetzner Provider Support)
• Depends on Add Provider enum and ProviderConfig types to domain layer #206 (Add Provider enum and ProviderConfig types)

[josecelano]

ACK 792e69d