Fix env variable bug and use docker hub image

[esteblock]

• IS_USING_DOCKER was not set. There was a bug when executing ./initialize.sh inside the docker image
• I propose to use the docker hub image esteblock/soroban-preview:7, so users don't need to build it for themselves.

[esteblock]

@paulbellamy , please check

[paulbellamy]

IS_USING_DOCKER is set in the Dockerfile itself, here: https://github.com/stellar/soroban-example-dapp/blob/main/Dockerfile#L19, so there's no need to pass it in separately.

[esteblock]

I understand. This is because I also proposed to use the esteblock/soroban-preview:7 docker image from Docker Hub. And that image does not have this env variable.

What do you think about using that image from Docker Hub? Also, with future previews, devs wont need to care too much about building the new image themselves.

If you think this is a good idea, I can add that variable in the image in DockerHub

[paulbellamy]

Isn't that image on dockerhub built from the same dockerfile? It would be nice if there were a traceability from that dockerfile through to the image on dockerhub so people have more confidence on the code they are running.

[esteblock]

Isn't that image on dockerhub built from the same dockerfile? It would be nice if there were a traceability from that dockerfile through to the image on dockerhub so people have more confidence on the code they are running.

They are published to dockerhub from https://github.com/esteblock/soroban-preview-docker/ Currently in that repo builders need to do

cd preview_7
bash build.sh
docker push esteblock/soroban-preview:7

But we can do this in a github action