feat(chat): update code search tool

[abeatrix]

https://linear.app/sourcegraph/issue/CODY-5542/experiment-with-grep-for-search

This commit introduces several enhancements to the code search tool used in the chat interface:

• Implements local search using grep or ripgrep for faster results within the codebase. It falls back to remote search if local search fails or returns no results.
• Adds schema options for include, exclude, and dir to allow users to specify file patterns and directories for the search.
• Updates the shell tool description to clarify its usage and limitations, emphasizing non-interactive commands and shell escaping.

These changes improve the efficiency and flexibility of the code search tool, providing users with more control over their search queries.

Test plan

Try asking Cody