Tracking Issue - Guided Tour / Help Center v1

Overview tracking issue for our Next Steps Guided Tour - paYE8P-1xk-p2.

## Glossary

We have three layers to our framework for Next Steps guidance:

```
Tutorial
|-- Task
|-- Step
```

## Tutorial

The top-level grouping of a collection of related Tasks. The three top-level Tutorials that will be going into the Help Center are 1) Site essentials, Homepage content, and 3) Launch site.

The most semantically useful umbrella term here would be **Tour** but that overlaps too much with the `TourKit` framework we will use for Steps. There was also of course [Guided Tour](https://github.com/Automattic/wp-calypso/blob/6cb33027cd048e31c0fbd065317cd4b9e17001e1/client/layout/guided-tours/README.md) in Calypso. There's even a backend email framework called Guides! There is no safe space, semantically speaking, in our codebases. So we settled on Tutorials as the least-occupied name.

## Task

A specific task to accomplish within the Tutorial. Examples in the above image include "Welcome to the site editor", "Personalize your site", "Give your site a name", and "Confirm your email address".

## Step

Each Task in a Tutorial will have one or more steps, rendered on the client by `TourKit`/`WpcomTourKit`. In the above example, there's a single step that will show a video for "Welcome to the site editor" Task. "Personalize your site" has 4 steps (not shown above), etc.

---

## Release Workflow
- [x] #65130

## Tutorial (formerly Checklist) API

- [x] #64251
- [x] #64252
- [ ] #64254

## TourKit

- [ ] #64256
- [ ] #64259

## Help Center / Next Steps Tour

- [x] Add help center to the Site Editor. (https://github.com/Automattic/wp-calypso/pull/63429)
- [ ] #64260
- [ ] #64261
- [ ] #64262
- [ ] #64263
- [ ] #64264
- [ ] #64265
- [ ] #64267
- [ ] #64334

## Guided Tour

- [ ] #64268
- [ ] https://github.com/Automattic/wp-calypso/issues/64374
- [ ] #64269
- [ ] #64335

## Testing and maintenance

- [ ] #64336
- [ ] #64337
- [ ] #64338

Start with the overview and glossary, then review the unchecked issues grouped under Release Workflow, Tutorial API, TourKit, Help Center / Next Steps Tour, Guided Tour, and Testing and maintenance. The tracking issue is complete when the remaining linked work is finished and the checklist is fully resolved.

Written by the indexing model from the issue text.