Feature 285/pydantic v2 config validation

[nmveeresh]

PR Summary: Enhanced Configuration Validation and Schema Export

Epic / Issue - #285

Overview

This PR implements comprehensive configuration validation and schema export capabilities for MCP Gateway. It provides operators with machine-readable configuration metadata and enforces stronger runtime validation for environment inputs, surfacing actionable errors early.

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Key Changes

1. JSON Schema Export (mcpgateway/config.py)

• Added generate_settings_schema() function to export the Pydantic model schema.
• Enhanced CLI with --schema flag to emit machine-readable configuration metadata.
• Enables automated validation in CI/CD pipelines.

2. Strengthened Field Validation

• Replaced string fields with Literal types for finite option sets (e.g., log_level, cache_type, transport_type).
• Added HttpUrl validation for URL fields (APP_DOMAIN, FEDERATION_PEERS).
• Implemented PositiveInt constraints for numeric ranges (e.g., PORT: 1-65535).
• Added SecretStr for sensitive fields to prevent accidental logging.
• Enhanced validators with clear error messages to stop misconfigured environments early.

3. Dedicated Environment Validation CLI (mcpgateway/scripts/validate_env.py)

• Standalone validation script with detection of weak/default secrets and other security warnings.
• Integrated into existing make check-env workflow.
• Supports validation of custom .env file paths.
• Provides actionable error messages with field-specific details.

4. Enhanced Makefile Integration

• Updated make check-env to use the new validation script for .env.example.
• Added make check-env-dev for validating development .env files.
• Fully integrated validation into existing developer workflows.

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Testing & Documentation

• Unit tests cover:
  • Schema export
  • CLI environment validation (valid/invalid cases)
  • Field-specific validation (URLs, enums, numeric ranges, secrets)
• Documentation added in docs/docs/operations/config-validation.md with usage examples and best practices.