Onboarding Existing Node-RED's - FlowFuse Plugin

## User Story

**As a Node-RED User, I want to connect my existing instance to FlowFuse without having to reinstall anything, so that I can manage my flows flows remotely**

The Node-RED will appear as a Remote Instance within the platform, albeit with a reduce set of functionality compared to a Device Agent managed Remote Instance.

## Roadmap Alignment

This aligns to the following areas of our strategy:

- Enables an onboarding journey for hardware with NR pre-installed where switching over to Device Agent is too high friction

## KPI

- The number of such plugins registered with a FF platform.

We will need to include stats for this in the telemetry ping to gather this data from self-hosted platforms.

## Phases

From the discovery work completed in #7439 we know there will be a functional gap between what the plugin can provide and the full Agent capability. A consequence of that is the platform needs to know the difference between a Device Agent driven Remote Instance versus the plugin. That is not something that can be iterated easily; it needs to know to hide/disable all unavailable features and then we can iterate on enabling them. That makes for a hard-to-avoid sizeable piece of enabling work up front.

_Aside: why require the connection to a FF Platform at all? All of the value-add we provide is tied to being a FF platform user; without that, we don't have a compelling value exchange in the plugin by itself to drive a sign up._

1. Create a NR plugin that provides a 'sign in to FlowFuse' button.
- It lets you sign-in to a FF account and uses the same Device Registration flow recently added to the Device Agent for onboarding
- Once connected, its status is shown in the FlowFuse UI
- No Remote Instance capabilities are enabled for the instance

2. Enable auto-snapshotting of flows
- when a user deploys new flows, generate a snapshot and save to the platform

This is the MVP of an iteration.

In parallel to doing this work, we will be able to identify other parts from the research work that can be enabled in subsequent iterations.