fix: need to check for submodule existence prior to docker image build

[qdzlug]

Describe the bug The Bank of Sirius submodule is a dependency for the project to build. This is addressed with logic in the start_all.sh script, with instructions being given for addressing the issue if it is encountered.

If the user chooses to use a docker image for deployment, what happens is that we create an image that does not contain the .git directory so the error will still be presented, but the user will not be able to address it (since the necessary git files are not there). So they will need to exit and rebuild the docker image, which is suboptimal.

We should do a check in the build script for docker to make sure the directory exists; this can be done at the same time as the fix for argument validation tracked in a different issue.

To Reproduce Steps to reproduce the behavior:

1. Clone repo w/o init of submodule
2. Build docker image
3. Run start_all.sh in docker image
4. Boom

Expected behavior We should throw an error when the user attempts to build the docker image, providing instructions on how to address.

Your environment

• n/a

Additional context None