[Research] Support for compliant secure storage

[vmutafov]

We should add the Vault in order to store internally used XSK user data in a secure way. We should consider whose responsibility would be to host the Vault, would it be the customer or we're going to host it in a container deployed with the XSK. The goal of this task would be to make the XSK authenticate itself against the Vault and provide a JS facade for the Vault HTTP APIs. The location of the Vault should be specified initially as environment variables.

[ThuF]

This should be considered as an “optional” dependency. The XSK should be able to run also without it.

[dpanayotov]

not relevant atm