Update the structured content result of the Codebase Search tool"

What does this MR do and why?

Remove the following fields:

• reindexing
• id
• type

Change the source field into different fields (see the chunk code for guide on how to split this field):

• blob_id
• start_byte
• start_line

How to set up and validate locally

reference the setup here: !205297 (comment 2756113040)

tiangao@tgao--20240202-M7DJJ ~ % rm -rf  ~/.mcp-auth                                                                                                                       
tiangao@tgao--20240202-M7DJJ ~ % npx @mcpjam/inspector  

and then go to : http://localhost:3000/#tools

connect to the mcp server:

   {
     "mcpServers": {
       "GitLab-Production": {
         "command": "npx",
         "args": ["-y", "mcp-remote@latest", "https://gdk.test:3443/api/v4/mcp", "--debug", "--static-oauth-client-metadata", "{\"scope\": \"mcp\"}"],
         "env": {"NODE_TLS_REJECT_UNAUTHORIZED": "0"}
       }
     }
   }

select the tool and run the following request:

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #575228