Implement get_merge_request_pipelines MCP Tool and service

Proposal

• Add support for new MCP tool: get_merge_request_pipelines which maps to `Merge Requests API - list merge request pipelines
• allow the following arguments from the API documentation
  • id (required)
  • merge_request_iid (required)
  • pagination parameters
• context response should contain either one of the following
  • "id1\nid2\nid3\n"
  • "id1: status1\nid2: status2\n"

JSON RESPONSE

[
  {
    "id": 77,
    "sha": "959e04d7c7a30600c894bd3c0cd0e1ce7f42c11d",
    "ref": "main",
    "status": "success"
  }
]