Docs: Add better/updated documentation of the events hierarchy of Dashboard 2.0

[joepavitt]

Description

I've had multiple people reach out asking for finer detail and clarity over the events architecture of Dashboard 2.0, especially detail on the state and data stores that exist on both client- and server- side.

This is the original events architecture diagram:

I also need to better document the lifecycle hooks APIs that exist for widgets too, and the default handlers, e.g. onInput in this diagram.

Example thread that raises this concern: https://discourse.nodered.org/t/vuejs-where-to-store-my-data/85939/8

Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate

[joepavitt]

First pass at improved/updated events architecture diagrams. I've made the call to split these into multiple images, rather than try and fit them all into one image like I do currently, which makes it overwhelming to rad, especially where the full diagram isn't actually connected.

Part 1. Deployment & Loading Logic

Part 2. Message Injection Logic

Part 3. Dashboard Actions Logic

[joepavitt]

This should also assist with #404