Add doc warning for risky plugin names (related to #1694)

[somsomin]

This PR resolves Issue #1694 by adding a warning for plugin folders named lib, test, or utils. These names may cause plugin loading conflicts due to Python module resolution or backend-specific files (e.g., Slack's lib.py).

I reproduced the issue by creating a plugin in a lib/ folder, which failed to load silently. I added a log.warning(...) message in plugin_manager.py to alert developers early. I also added a documentation warning in docs/plugindevelopment.rst to guide plugin authors.

Let me know if you'd like anything adjusted.

[nzlosh]

If you intended to push code changes to this PR, you should adjust the title as it no longer only addresses documentation.

[sijis]

This unfortunately would break the usage in

errbot/errbot/plugin_manager.py

Lines 317 to 338 in 3c3af1a

	def _load_plugins(self) -> Dict[Path, str]:
	feedback = {}
	for path in self.plugin_places:
	self._load_plugins_generic(
	path,
	"plug",
	"errbot.plugins",
	BotPlugin,
	self.plugins,
	self.plugin_infos,
	feedback,
	)
	self._load_plugins_generic(
	path,
	"flow",
	"errbot.flows",
	BotFlow,
	self.flows,
	self.flow_infos,
	feedback,
	)
	return feedback

, as the parameters being passed include plug and flow. This change, unfortunately does not address that and include a new one named plugin.

[sijis]

This warning can be very useful for plugin developers.