Make --log-format=internal-json externally accessible

[DieracDelta]

Is your feature request related to a problem? Please describe. I'd like to consume nix build information without being attached to stdout.

Describe the solution you'd like I could see two ways for this to work:

• structured output via gRPC over http
• writing the logging to a (probably very large) file in tmp when a flag is toggled

Either would be super useful for me.

Related: Could I implement this and make a PR? Or would I need to draft up an RFC first? (I'm new to contributing and not familiar with the process)

Describe alternatives you've considered N/A

Additional context N/A

Priorities