[services][backup] Use Rust service in Dockerfile

Summary:
Resolves ENG-2701

• Mostly copy-pasted Dockerfile from Blob service
• Made it more flexible by moving LOCALSTACK_URL and BLOB_SERVICE_URL to docker-compose.yml config
• I left COMM_SERVICES_SANDBOX handled internally in-app, because it is more flexible - distinguishes truthy and falsy values - see this line

Depends on D6246

Test Plan:

cd services
yarn init-local-cloud

# now this also starts blob service automatically
# no need to run 'yarn run-blob-service'
yarn run-backup-service-in-sandbox

# in a separate terminal
yarn run-integration-tests backup

Reviewers: jon, varun, tomek

Reviewed By: jon

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D6262