Add a mechanism to override all of the relay's env variables without explicitly exposing them manually

[natanasow]

Problem

Currently, there is no natural way to override a relay's env if it's been added recently and not manually exposed in the local node as a config variable. All of the available overrides are described here and they are mapped to the relay's container here, again manually.

Solution

Should add an ability to pass an entire user's defined .env file (or single a single env variable) to the relay's container.

Alternatives

No response