slim-onbuild tag

[soullivaneuh]

Would be great to have a tag with a combination of slim and onbuild tags to save space.

I did it manually on maildev/maildev#102 and it works perfectly.

[retrohacker]

I think this has been brought up before, but I'm failing to dig up the issue.

If memory serves, we were 👎 on adding an extra tag. The onbuild tag is opinionated and, while we support it, we don't recommend it for most use cases. We were 👎 on increasing the number of images we support for the onbuild tag.

If memory serves, @Starefossen had some strong feelings on this.

[Starefossen]

Yes, the onbuild is a great tag but it is terrible misused and even discouraged by official Docker recommendation for use in production environments. See #66 for more details.

[chorrell]

Yeah, the general consensus was we were 👎 on adding another variant