[12.0] Support merge request dependency endpoint

[kayw-geek]

Support Merge Request Dependencies API

🎯 Overview

Add comprehensive support for GitLab's Merge Request Dependencies API, enabling developers to manage blocking relationships between merge requests programmatically.

✨ Features Added

New API Methods

• createDependency() - Create dependency between merge requests
• dependencies() - List all dependencies for a merge request
• deleteDependency() - Remove dependency relationship
• blockedMrs() - Get merge requests blocked by current MR

API Endpoints Covered

POST   /projects/:id/merge_requests/:merge_request_iid/blocks (The example in the official document is wrong.)
GET    /projects/:id/merge_requests/:merge_request_iid/blocks
DELETE /projects/:id/merge_requests/:merge_request_iid/blocks/:block_id
GET    /projects/:id/merge_requests/:merge_request_iid/blockees

Related: GitLab Merge Request Dependencies API Documentation

[kayw-geek]

Hey @GrahamCampbell, could you take a look at this when you get a chance? Thanks!