Leverage gitlab_search MCP tool in DAP

Problem

Agentic Chat cannot do multi-project search in a group namespace, lacking tool support.

Proposal

The gitlab_search MCP tool was implemented in #571132 (closed) which allows users to scope searches to specific groups and projects, not just global searches. The tool automatically routes your request to the right API based on what you provide. It supports cross-group or instance level searches.

Let's add the gitlab_search tool to the list of enabled MCP tools in DAP and provide it to agentic chat.