Packaging and deployment

[sjahl]

Just realized that I hadn't PR'd this yet. As a reminder for if/when someone needs to pick this up, this is currently deployed at https://sumstats.gnomad.the-tgg.dev/, with the deployment definition living at broadinstitute/gnomad-deployments#6

This PR adds:

• a Dockerfile and .dockerignore for building/deployment
• A cloudbuild definition to build and push the image to artifact registry

And:

• rewrites the requirements.txt file using a fully locked version via pip-tools to match requirements-dev.txt
• uses requirements.txt as a constraint for requirements-dev to reduce conflicts between the two.