docs: prod achitecture overview

[alexgarel]

What

Overview of the target architecture for production.

Best viewed at https://github.com/openfoodfacts/openfoodfacts-infrastructure/tree/docs-infra-overview/docs

Part of:

• Document our target infrastructure in order to discuss and share the same vision #190

[alexgarel]

@stephanegigandet @CharlesNepote @cquest you can already comment.

I want to add a diagram for storage (mostly ZFS organization). (the actual one, is more about network).

[alexgarel]

Discussion with @CharlesNepote

On diagram:

• Apache --> apache (product opener/perl)
• Make two arrow on user
• add OVH - Free: séparation
• add images (and ovh3)

Explain double NGINX

Link zfs datasets to official docs

[alexgarel]

I'm merging this although it's a work in progress to avoid a long PR.