change(docs): Update 'Design Overview' page of Zebra book

[arya2]

Motivation

We want to update the design overview page with some notable blog posts and a graph of service dependencies to help new developers understand zebrad faster.

Closes #2740.

Solution

• Add links to notable blog posts
• Add a simplified graph of service dependencies

Related changes:

• Correction of issue/PR references in Pipelineable Block Lookup RFC
• Remove some out-of-date text

Review

Anyone can review.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
  • Does it change concurrent code, unsafe code, or consensus rules?
• How do you know it works? Does it have tests?

[arya2]

Here's the input for the graph:

digraph services {
    state -> transaction_verifier
    state -> mempool
    state -> chain_verifier
    transaction_verifier -> mempool
    transaction_verifier -> chain_verifier
    mempool -> inbound
    chain_verifier -> inbound
    chain_verifier -> syncer
    inbound -> peer_set
    peer_set -> syncer
    peer_set -> mempool
}

Rendered here

I tried making it comprehensive at first but it seemed to grow unnecessarily complicated, so I left in what I thought would be most useful.

I'm open to suggestions on what should be included.

This is what looks like rendered in the dark themes*:

*in most browsers, see https://caniuse.com/css-filters

[teor2345]

Thanks, looks great!

There are no blockers here, except for an arrow on a diagram that I think is the wrong way around?

[teor2345]

Can you add the source of the diagram and the online tool you used to generate it in a markdown comment?
(I think they work the same as HTML comments.)

That way, anyone can edit the diagram if they want.