Support for better appliance scalability/HA/clustering support - i.e. make it easier to "split" a single app between separate servers

[JedMeister]

For example, it would be nice to make it easier for users to be able to host the primary TurnKey appliance webapp on one server and the database on another server. And/or have a multi-region and/or HA (high availability) multi server setup.

To quote @marcos-mendez from #1831 (comment) - this specifically relates to our Odoo appliance, but applies generally IMO:

Decoupling PostgreSQL from the Odoo appliance

Another topic I want to raise, because it connects directly to the scalability discussion: we need to work toward making PostgreSQL decoupled from the core Odoo appliance at some point. At PopSolutions we run Odoo instances serving 4,000+ concurrent users, and the single-node PostgreSQL bundled in the appliance simply does not scale to that level. What we need is the ability to point the appliance at an external PostgreSQL cluster — ideally with primary/replica topology for read scaling and HA.

FYI I wasn't sure exactly how to tag this, but I chose "Core - base (all apps)" and "common" because I'd like to see it applied across the appliance library as much as possible (hence much - if not all in the "common" rep). I included "odoo" too because that is the specific use case noted in the above quote from Marcos (and likely where the initial energy to develop this is going to come from).