DOCS: Deploy the demo app, connected to DevNet

# Background

Create content that corresponds to the section: [Deploy the demo app to DevNet](https://docs.google.com/document/d/1XauuMZaR-TtPmk9Ux1rKiRLA-vTKcFTkWjY7xhTtSYk/edit?tab=t.0#heading=h.7tjal4zfcmap)

Prior art to see sample of RST format: [Read API](https://github.com/DACH-NY/scribe/blob/85d378f056e3a3300718bcaaa470410d2c7fb733/docs/user/01-build-howto-integrate.rst#L5)

# More Information Needed

Needs more clarification to understand how this tutorial would be constructed:
* How is this envisaged? Deploy into what infra environment?
* Being a tutorial it needs to be very specific, and tangible - specific commands and expected outcomes.
* What assumptions would be made in the deployment environment? We did something similar for Spider, but this involved a multi-step Quickstart equivalent where the user could step-by-step conduct a setup of a system. Even then it didn't contemplate K8S or similar, as that was wired into client concerns.
* We are trying to envisage how this would be better than inspecting QS/LocalNet via docker-compose setup, and examining it as a container deployment (albeit on a single host).
* Is there something like this for Canton/Canton Network to use as a guide for better understanding the intent?
* How does this relate to QS, other than the fact of "Demo App" (I presume this is QS app).

# Task

* Assemble new content in CN-Quickstart repo: `/docs/user/qs-deploy-the-demo-app-to-devnet.rst`. This is a temporary name that will be aligned with the directory hierarchy of the docs repository, and once we know that we will provide it to you.
* Content:
* step by step deployment of demo app to DevNet
* outline tutorial, review with [jp.miller@devdocs.work](mailto:jp.miller@devdocs.work) and editors
* write
* ensure it is covered by automated tests