Add Debugging Instructions to Devcontainer Setup in CONTRIBUTING.md

[m3hm3t]

Description:
This PR adds a section to CONTRIBUTING.md that explains how to set up debugging in the devcontainer using VS Code.

Changes:

• New Debugging Section: Clear instructions on starting the debugger, selecting the appropriate PostgreSQL process, and setting breakpoints for easier troubleshooting.

Purpose:

• Improved Contributor Workflow: Enables contributors to debug the Citus extension within the devcontainer, enhancing productivity and making it easier to resolve issues.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.69%. Comparing base (9e1852e) to head (b096b85).
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Additional details and impacted files

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[thanodnl]

Although this works great when having a single psql session open, it fails when multiple sessions open, or when you are connecting over the tcp stack instead of the named pipe.

Not saying to remove this, as it could cover a good portion of the simple workflows.

However, it would be great to add a section on the pid of the backend you are connected to. When running in the devcontainer a .psqlrc is installed in the devcontainer which changes the prompt of psql to show the pid of the running process.

citus@07de2e6180a9:/data$ psql
Timing is on.
Line style is unicode.
Border style is 2.
psql (16.2)
Type "help" for help.


[local] citus@citus:9700-3783=# 

The last number in the prompt, 3783 is the pid of the backend that psql session is connected to.

If you have the process selector open for the debugger you can simply type these numbers, which is generally easier than typing the name of the process - although a tactical [local] will filter it down to the sessions connected via the named pipe.

[m3hm3t]

Thanks for the feedback! @thanodnl

You're right, this method works well for simple workflows with a single psql session but can be tricky when dealing with multiple sessions or TCP connections. I added a section to clarify how to locate the pid of the backend you're connected to in the container setup. The .psqlrc prompt tweak showing the pid is a great tip—I included it.