Setup Azurite for local Azure Blob Storage testing

[hubertp]

Testing Azure Blob Storage currently requires real credentials to Azure account. We still want to test integration but for regular tests it would be sufficient to use local storage emulator.

Turns out Azurite provides such Azure compatible API and could potentially satisfy the requirements.

1. Setup docker with Azurite in a CI job, prior to running tests
2. Setup correct credentials
3. Make endpoints configurable so that tests refer to a local storage (there are some differences)