[Client guide] Extend/rework the user journey with "feature overview" pages

[trwnh]

#1896 alphabetizes a previously mostly-structured menu for the API methods, which is a fine change for purely reference-based workflows, but it would be nice to have that old structure preserved somewhere else.

The current (old) ordering sorta follows a journey of how you might want to implement certain API features. I think it could be handled by reworking the /client/ ("Developing Mastodon apps") section to include "feature" pages, but I never got around to that.

So for example:

• apps is first because you need to register your client.
  • oauth is nested under that because you will probably need to obtain tokens for your client or anyone using your client.
• accounts was second because once your client has users, it makes sense to register accounts, verify credentials, browse profiles, etc.
  • Various API routes related to your account are nested under that -- bookmarks, favourites, mutes, blocks, filters, etc
• statuses for when your users were ready to start posting
  • media attachments, polls, and scheduled_statuses are likely to be used while posting
• timelines for when your users want to view multiple statuses
  • lists, markers, streaming were also relevant when working with timelines
• notifications as the next thing to deal with
  • push notifications being a subset of that
• search as the last remaining thing a user might do
• instance for anyone wanting to get info about the instance itself
  • trends and the profile directory were also instance-wide features, etc
• admin for all the admin stuff which most users wouldn't need to use
  • all the stuff prefixed with admin/

If you look at the end of a page like https://docs.joinmastodon.org/client/authorized/ you can see a sort-of skeleton of the same rough concept that never got expanded on. It could be worthwhile to expand this out from a list into "feature" pages just like what was done with quote posts. So you'd have the existing "public" -> "authorized client" -> "authorized user" journey, but extend it with a feature-by-feature breakdown.