Add Debugging Instructions to Nix Manual

[michaelvanstraten]

Problem

Currently, it's hard to get started with launching a debuggable instance of Nix. Building Nix with debug symbols requires knowledge of internal environment variables like mesonBuildType, which are not well-documented. For example, to build with debug symbols, you need to run:

nix develop .#native-clangStdenvPackages
# `make clean` did not work
trash build 
export mesonBuildType=debug
mesonConfigurePhase
ninjaBuildPhase

Additionally, there is no documentation on how to attach a debugger to the nix-daemon.

Proposal

Add a "Debugging" section to the Nix manual's development chapter. This section should include:

• Detailed instructions on how to build Nix with debug symbols, etc.
• Step-by-step guidance on how to launch and attach a debugger to debug version ofnix-daemon.

Checklist

• [x] Checked latest Nix manual (source)
• [x] Checked open documentation issues and pull requests for possible duplicates

Priorities

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[michaelvanstraten]

I am planning to create a pull request to add this documentation if it hasn't been done already.