epic: code quality

[bgauduch]

Status tracked in #106.

Objective

Fix the technical debt in dev.sh and the Dockerfile, and extend the container structure-test coverage.

Tasks

dev.sh

• Implement getopts for argument parsing (existing FIXME)
• Add semver validation of arguments (existing FIXME)
• Fix the PLATEFORM → PLATFORM typo
• Add set -euo pipefail and clean error handling

Dockerfile

• Merge the separate RUN apt-get install in the terraform and aws-cli stages (reduce the number of layers)

Tests

• Extend container-structure-tests.yml.template: negative tests (verify the root user is not used), check binaries are in PATH