Define missing MCP tools for /mcp_server

What does this MR do and why?

The current MCP server implementation defines multiple tools: https://docs.gitlab.com/user/gitlab_duo/model_context_protocol/mcp_server/#connect-cursor-to-a-gitlab-mcp-server. Let's also define them using new approach. After it's verified, we can switch the existing endpoint /api/v4/mcp to the new implementation.

The new approach introduced in Define an MCP tool via API setting (!201838 - merged), allows us to specify to following line to define a toll:

route_setting :mcp, tool_issue: ..., params: ...

The list of tools defined:

• get_pipeline_jobs
• create_issue
• get_merge_request_commits
• get_merge_request_diffs
• get_merge_request_pipelines