feat: add protected environments API support

[vish288]

Summary

GitLab exposes protected environments via the REST API (docs), but the MCP server has no tools for managing them.

Requested Tools

Tool	API Endpoint	Description
gitlab_list_protected_environments	GET /projects/:id/protected_environments	List all protected environments
gitlab_get_protected_environment	GET /projects/:id/protected_environments/:name	Get a single protected environment
gitlab_protect_environment	POST /projects/:id/protected_environments	Protect an environment with deploy/approval rules
gitlab_update_protected_environment	PUT /projects/:id/protected_environments/:name	Update deploy access and approval rules
gitlab_unprotect_environment	DELETE /projects/:id/protected_environments/:name	Remove environment protection

Key Use Cases

• Add/remove deployment approvers (users or groups) for protected environments
• Set required approval counts for deployments
• Manage deploy access levels (maintainer, developer, specific users)
• Automate environment protection setup for new projects

Context

Currently the only way to manage deployment approvers is through the GitLab UI (Settings > CI/CD > Protected environments). Having MCP tools for this would allow full CI/CD configuration management without leaving the editor.