Spinup container with a rofl app in the CI tests

[ptrus]

We run a simple test in CI to ensure localnet docker image is working as expected: https://github.com/oasisprotocol/oasis-web3-gateway/blob/main/docker/sapphire-localnet/test.sh

Inslude a ROFL artefact in the test, so that it covers a larger surface. (it detects things like: #659)