Onboarding: FlowFuse Cloud

### Description

An Epic to track general improvements and ideas to reducing friction in the onboarding to FlowFuse.

The purpose of this epic is to identify ways to increase Time to Value for new FlowFuse users.

User onboarding covers the user's actions from the time the not-yet-user lands on our webpage, and seeks to guide the user to value as effectively and quickly as possible.

This epic addresses several gaps in the new user onboarding funnel.
- 60% of visitors who visit the Sign Up page do not sign up. This will be addressed in FlowFuse/flowfuse#1806 and can be improved by 10% by implementing social sign-in.
- Only 20% of users who clicked 'Add Remote Instance' successfully opened Developer Mode, which is required to manage Node-RED instances running on edge devices. This number should be close to 100%. This is addressed in [#401](https://github.com/FlowFuse/device-agent/issues/401)
- Since returning to the Team trial (and away from letting users choose any tier upon signup), the percentage of users [opening the editor within one hour of signing up is around 60%](https://eu.posthog.com/project/2209/insights/CDIGyApf). We can improve that number another 20% by leading the user to connect existing Node-REDs running elsewhere. This is addressed in FlowFuse/product#3 , and also by FlowFuse/flowfuse#5580 , as most users cancel the new user product tour and never have their first instance highlighted.
- Relatedly, FlowFuse/flowfuse#3666 will make building in Node-RED even easier by allowing subflows to function as snapshots.

Related:

- FlowFuse/flowfuse#4913
- FlowFuse/flowfuse#4914

Previous work:

```[tasklist]
- [x] https://github.com/FlowFuse/flowfuse/issues/2721
- [x] https://github.com/FlowFuse/flowfuse/issues/3884
- [x] https://github.com/FlowFuse/flowfuse/issues/4039
- [x] https://github.com/FlowFuse/flowfuse/issues/4168
- [x] https://github.com/FlowFuse/flowfuse/issues/4169
- [x] https://github.com/FlowFuse/flowfuse/issues/4197
- [ ] Drop new users straight into the Immersive Editor
```

### Which customers would this be available to

None
```[tasklist]
### Ideas
- [ ] https://github.com/FlowFuse/flowfuse/issues/3901
- [ ] https://github.com/FlowFuse/flowfuse/issues/3917
- [ ] FlowFuse/flowfuse#1806
```