silence pylint warning about pika dep in tool

[cognifloyd]

Every now and then, pylint gets upset about a pika import in tools/direct_queue_publisher.py. Here's a snippet from a GHA run in #5096 (NB: that PR does not touch any of these files, so fixing this in that PR doesn't make sense):

. virtualenv/bin/activate; pylint -j 4 -E --rcfile=./lint-configs/python/.pylintrc --load-plugins=pylint_plugins.api_models tools/*.py || exit 1;
************* Module tools.direct_queue_publisher
tools/direct_queue_publisher.py:21:0: E0401: Unable to import 'pika' (import-error)
make: *** [Makefile:351: .pylint] Error 1

https://github.com/StackStorm/st2/pull/5096/checks?check_run_id=3808812826#step:11:467

st2/tools/direct_queue_publisher.py

Line 21 in 8496bb2

import pika

I think it's weird that we're not consistently getting this error because pylint should be running on all the tools files:

st2/Makefile

Line 361 in f65f62f

. $(VIRTUALENV_DIR)/bin/activate; pylint -j $(PYLINT_CONCURRENCY) -E --rcfile=./lint-configs/python/.pylintrc --load-plugins=pylint_plugins.api_models tools/*.py || exit 1;

This tool dates back to April 2016 (f6897d2) with this in the commit message:

• Exisiting tool queue_producer published to an exchange. This is for direct publishing to a queue.
• Written on top of pika instead of kombu as this was simpler to write given code samples on rabbitmq tutorial site

Plus, from what I can tell, kombu doesn't offer a way to publish directly to a queue; it requires an exchange. So this tool has to use something other than kombu.

So, we can either delete this script or leave it around for possible future debugging. To leave it around, we should protect it such that pylint doesn't complain and anyone who tries to use it gets a helpful message about why it doesn't work. That's what I did in this PR.

[amanda11]

LGTM, but could you also add a changelog entry,