Reduce boilerplate: Move comment script out of this repo

[stevector]

Here is a break-out issue from #61 (comment)

The file add-commit-comment does not need to be specific to this repo. It could be moved to inside a Docker container after #107 lands or to a shared Composer project.

[stevector]

Ah, I think @greg-1-anderson intends to put this script inside the build tools plugin.

[greg-1-anderson]

Correct, Lukas is working on this. We can leave this issue open for tracking.