feat: Add default context exclusions for filesystem tools

Erran Careyrequested to merge
erran/add-default-filesystem-tools-context-exclusions into main

What does this merge request do and why?

feat: Add default context exclusions for filesystem tools

Ensure language server clients without support for Duo Context Exclusions respect defaults through server-side exclusions for filesystem tools.

Close https://gitlab.com/gitlab-org/modelops/applied-ml/code-suggestions/ai-assist/-/issues/1185.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

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

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