config: support excluding images in environment variable.

[gabay]

NOTE: I read your note about pausing cup development. this PR is of no urgency whatsoever.

I came across a need to ignore just one image, and didn't want to create a config file just for that

example use in docker compose file - ignore postgres:16 and postgres:17 images:

cup:
        ...
        environment:
            CUP_IMAGES_EXCLUDE: postgres:16,postgres:17

[sergi0g]

Hey @gabay, thanks for taking the time to create this PR! I'm finally done with my final exams, so I hope to start working on Cup again soon (in addition to some other projects) and I'll probably completely rewrite it. I don't know if that will ever succeed or when, so I think we should get this merged.

From my first really quick review (I'm not on my computer right now, sorry), I'll say the following:

• I think it may be better to separate references with spaces, so somebody reading a compose can easily see where one reference ends and the other begins instead of trying to find commas in a (probably) large blob of text. This should tolerate multiple spaces between references too, as it is easy for one to accidentally slip through.
• It seems your formatter may have changed a few things in other files too. I'd ideally like only functional changes in this PR. I normally format everything with cargo fmt.

I'll do a more thorough review later. It'd be great if you could fix these in the meantime!

[gabay]

thanks for replying, I hope the exams went as well as could be :)

• Removed all non-relevant changes (except the ability to debug-print the config - I find it extremely useful).
• Changed the format to be space-separated instead of comma-separated.
• tried cargo fmt but it's misbehaving, sorry in advance if I missed something.

BTW - I used AI to create the initial draft for tis PR. IDK what's your take on it, I prefer to be clear about that.