FR: make testing custom PRs easier

[barnabasbusa]

Background & motivation

Currently it is rather difficult to test a random PR on the kurtosis repo.

To test this, it either involves a deep dive into the world of Nix (which is not something most people would like to have a deep dive on, if they just want to test a PR).
Or they have to ask a developer like @h4ck3rk3y to locally build a new engine image, and pull that, retag it, and trick kurtosis into thinking that is the image that should be used.

Current method is ugly, and time consuming:
Assuming the docker image is available on h4ck3rk3y/xyz:store

kurtosis engine stop
docker pull h4ck3rk3y/engine:store 
docker pull h4ck3rk3y/core:store 
docker pull h4ck3rk3y/files-artifacts-expander:store

docker tag h4ck3rk3y/engine:store kurtosistech/engine:c2cf7d-dirty 
docker tag h4ck3rk3y/core:store kurtosistech/core:c2cf7d-dirty
docker tag h4ck3rk3y/files-artifacts-expander:store  kurtosistech/files-artifacts-expander:c2cf7d-dirty
kurtosis engine restart --version c2cf7d-dirty

Desired behaviour

I would prefer to have a simple dockerfile, which could be built with docker build . -t feature/branch

Then run kurtosis with kurtosis run ... --custom-image feature/branch

If this additional flag could be added, then CI workflows could be tested with custom PRs, and this could mean that external packages like the ethereum package could be tested with a feature branch of kurtosis.

How important is this to you?

Critical; Kurtosis is unusable for me without it.

What area of the product does this pertain to?

CLI: the Command Line Interface

[barnabasbusa]

An example PR that would need to run a feature branch of kurtosis is: ethpandaops/ethereum-package#582