Dashboard Migration Service

### Description

With a `0.0.1` version of https://github.com/FlowFuse/node-red-dashboard-2-migration published, we should provide a web service to allow users to upload a `flow.json`, run their flow through our migration library, and then receive (probably via e-mail for leads) a migrated `flow-dashboard2.json`

Likely that this will be tightly linked with https://github.com/FlowFuse/website/issues/2131

### Epic/Story

_No response_

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

I have provided an initial effort estimate