feat: enable blob_search tool

What does this merge request do and why?

This change adds a new search capability called "gitlab_blob_search" to three different tool lists across two workflow files. The new tool is being made available to chat workflows, software development workflows, and context building processes, allowing these systems to search through code files (called "blobs" in Git terminology) within GitLab repositories. This enhancement expands the search functionality beyond just issues, merge requests, and documentation to include searching through actual source code files.

How to set up and validate locally

1. Set up Zoekt using this guide
2. Check out to this merge request's branch.
3. Start the workflow service
4. Ask the agentic duo chat to answer a question about the repository
5. It should use the new tool and search for exact matches in the repository

Example from the demo: gitlab-org/gitlab#541479 (comment 2633789102)

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.