[FEATURE] Support integration with CI/CD pipelines

[duaraghav8]

Is your feature request related to a problem you're facing?
I don't know for sure whether dockershrink can work well with CI/CD pipelines today or not.
One thing it does take care of is to exit with code 0 in case of success and non-0 in case of failures.
But how do we treat warnings? Recommendations? Needs to be discussed

Describe the solution you'd like
Ideally, a user must be able to integrate dockershrink into their container image-building pipeline (before running docker build or equivalents).
If dockershrink could not find ANY optimizations to make, the pipeline should proceed.
But if optimizations are possible, it must fail the build pipeline or at least produce a warning (configurable by user).

Optionally describe alternatives you've considered
Run the tool locally to optimize the image. Only when DS no longer has anything to change do I push the code and begin building process.

[rssnyder]

But if optimizations are possible, it must fail the build pipeline or at least produce a warning (configurable by user).

Sounds like you would need a -check command which would return non-0 in the case that optimization was possible, and 0 otherwise. Then in your pipeline simply have a step that runs dockershrink -check.

We do this today with tofu fmt -check

[duaraghav8]

Agreed, this is the behavior required.
Regarding the name of the flag, I also like something like --ci (dockershrink optimize --ci), simply because it is easier to guess the purpose of this option