Improve documentation about Config objects

[WardLT]

Description

Dole out content and explanations about Config objects in smaller chunks.

• Explain the difference between Config, Executor, Provider, and Launcher
• Give a quick overview of how to select Executor, Provider, and Launcher separate from details
• Explain which Executor features relate to HTEx or WQEx
• Move the data stuff to it's own "advanced" section (triaging it for now)
• Spread out and refine the explanatory text of blocks/parallelism

Changed Behaviour

N/A

Fixes

Part of #3781

Type of change

• Update to human readable text: Documentation/error messages/comments

[WardLT]

I'm realizing that I should mention the other features of a Config object, especially restarting and usage tracking. I'll get at added this week

[WardLT]

Alright, @kylechard or @benclifford , any advice on who I should get to review this?

It does break the "one bullet point per PR" Ben referenced in #3783 . I'm happy to break into small PRs. This was larger than I hoped it to be as breaking off new sections required adding introductory content

[WardLT]

Alright. I made another editing pass after filling in the placeholder for WorkQueue.

Should I recruit someone for reviewing this?