feat(api): add external api endpoints for interact with rustmail via external system

[Akinator31]

This pull request introduces a comprehensive API key management system and adds support for external ticket creation endpoints. The main changes include a new database schema for API keys, handlers for creating, listing, revoking, and deleting API keys, middleware for API key authentication and permission checks, and new routes for both API key and external ticket operations.

API Key Management

• Added a migration script to create the api_keys table, including fields for key hash, permissions, expiration, usage tracking, and relevant indexes for performance.
• Implemented handlers for creating (create.rs), listing (list.rs), revoking (revoke.rs), and deleting (delete.rs) API keys, supporting permission assignment and key lifecycle management.

Authentication and Permissions

• Updated the authentication middleware to support API key authentication via the x-api-key header, including key validation, usage tracking, and error handling.
• Added permission middleware and utility functions to check API key permissions for protected endpoints, returning standardized error responses when permissions are missing.

Routing and Integration

• Introduced new API routes for API key management (/api/apikeys) and external endpoints (/api/externals), with appropriate middleware protection.

Dependency Updates

• Added new dependencies (prefixed-api-key, sha2, hex) to support secure API key generation and hashing.