Statement that reads an arbitrary file and merges the content with the input already read by restroom-mw core

[andrea-dintino]

A VM-let will need to sign output and possible use ZKP. Each VM-let will have its own keyring and set of credentials: this data needs to be static and needs to be consumed by different Zencode scripts. Since for each script.zen restroom-mw will load the script.keys, we need to introduce a third input channel, specifically for the keys and credentials.

Therefore we need a statement, implemented in the files middleware, that reads an arbitrary file and merges it with the rest of the input. In case of namespace conflicts, the statement should overwrite the existing data (specifically the keys:{} object). For security reasons, it's desirable to have the file name inline, with an extension different from .keys (so restroom-mw core will never read it)

The statement could be:

GIven I read the the content of './keyring.json'