chore: add .fdignore file to allow fd in src

[xmfcx]

Signed-off-by: M. Fatih Cırıt mfc@leodrive.ai

Description

https://autowarefoundation.github.io/autoware-documentation/main/how-to-guides/applying-clang-tidy-to-ros-packages/#usage

I was trying to follow clang-tidy -p build/ $(fd -e cpp -e hpp --full-path "/autoware_utils/") command, I've realized because of the .gitignore file, /src/ was being ignored.

With this pr, fd command will work as expected with the added .fdignore file.

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[kenji-miyake]

The same as .rgignore added in autowarefoundation/autoware_core_universe_prototype#121

[kenji-miyake]

@xmfcx Since it's not a feature, I changed the title to chore.