Enforce consistent channel ordering in Pixie

[alex-l-kong]

What is the purpose of this PR?

Users may not always specify channels in strictly alphabetical order when running pixel-level Pixie. Additionally, Python's definition of sorting differs significantly from how we normally think of sorting, especially with capitalization. To prevent confusion, we need a consistent, non-stochastic ordering of channel names.

How did you implement your changes

Add a line to call Python's sorted function after defining the channels list. This ensures channels adheres to Python's sorting conventions.

Remaining issues

Not sure if cross-platform compatibility will be an issue, but sorted should be OS-agnostic.

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[cliu72]

@alex-l-kong I thought this was already addressed in this PR: #1114 (See point that says "Adds natsort calls throughout the Pixie pipeline to avoid issues with channel ordering." under "Pixel clustering"). Does this PR address something different?

[alex-l-kong]

@alex-l-kong I thought this was already addressed in this PR: #1114 (See point that says "Adds natsort calls throughout the Pixie pipeline to avoid issues with channel ordering." under "Pixel clustering"). Does this PR address something different?

Let me check with Avery again. It looked like he had updated the repo but he was still running into this issue, so I added this as an additional safeguard.