add debug flag to 'plural cd services lua' command

[zreigz]

Summary

This PR updates the Lua state initialization to register a custom print() function that writes all Lua output to a Go bytes.Buffer. This allows capturing printed output from Lua scripts for debugging

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• If required, I have updated the Plural documentation accordingly.
• I have added tests to cover my changes.
• I have added a meaningful title and summary to convey the impact of this PR to a user.
• I have added relevant labels to this PR to help with categorization for release notes.

[michaeljguarino]

Isn't print a lua built-in? I think all we need is to ensure it actually gets sent to os stdout. This is fine if it works, just seems like it might not be necessary

[zreigz]

@michaeljguarino but we want to display stdout conditionally, depending on the debug flag, right?

[zreigz]

Stdout is now captured and shown only when debugging is enabled

[michaeljguarino]

I actually don't fully grok what this is doing. Is the idea that you're directing stdout to the pipe (which is going to receive the lua print built-ins) and then only actually printing it if debug is enabled?

[zreigz]

Generally, yes, so the question is, how should it work?

[zreigz]

Should I add extra Go print, for example:

	luaFile := c.String("lua-file")
	if debug {
		fmt.Printf("luaFile: %s\n", luaFile)
	}
	context := c.String("context")
	if debug {
		fmt.Printf("context: %s\n", context)
	}

[michaeljguarino]

The way it should work is any invocation of print within a lua script should actually go to stdout instead of being swallowed. I'd assume the lua engine does that directly but apparently there's some issue with the way it currently works.

[zreigz]

Exactly, the Lua engine sends the output of the built-in print function to stdout, so the issue was a bit misleading for me because I didn’t understand why the --debug flag was needed. I’ll take a closer look and try to reproduce the problem. If you have a faulty script that demonstrates this issue, it would be very helpful