Closes #33286

This PR adds support for Zed's `$ZED_PICK_PID` command in debug
configurations, which allows users to select a process to attach to at
debug time. When this variable is present in a debug configuration, Zed
automatically opens a process picker modal.

Follow up for this will be integrating this variable in the task system
instead of just the debug configuration system.

Release Notes:

- Added `$ZED_PICK_PID` variable for debug configurations, allowing
users to select which process to attach the debugger to at runtime

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Co-authored-by: Remco Smits <djsmits12@gmail.com>