Add "Import Snapshot" Endpoint to the FlowFuse API

### Description

In order to be able to deploy an application across VPC clusters in Kubernetes, as a Developer, I would like an endpoint in the FlowFuse API that would allow me to import a previously exported application snapshot.

We’ve been working with FlowFuse for the last few weeks now, as part of an investigation into how it, and Node-RED could be used in our organisation.

We like the speed at which a developer can create an application using FlowFuse and Node-RED so naturally, we were interested in using the DevOps pipelines feature. However, due to restrictions placed upon us for security reasons, our non-prod and prod Kubernetes clusters are in differing VPCs and have no network connectivity between them.

This makes deploying Node-RED applications via a FlowFuse DevOps pipeline impossible as we’re not able to assign a production instance to an environment as it would exist outside of the k8s cluster that FlowFuse is running on.

A potential solution would be to use a third-party tool that can export a snapshot from an application in one instance of FlowFuse and then import it into application of another instance. For example, for our traditional use case, we employ Octopus Deploy to create deployment pipelines for artefacts into our non-prod and prod environments.

We have noticed that the FlowFuse API has an endpoint for exporting application snapshots, however, we cannot use this approach as currently there isn’t an endpoint for importing snapshots.

As I am not a member of FlowFuse, I'm not able to suggest an estimate, nor give any indication as to which customers this feature would be available to.

### Which customers would this be available to

Other (See comments)

### Have you provided an initial effort estimate for this issue?

I am not a FlowFuse team member