Update proof of stake section (wiki migration)

[jmcook1186]

Description

This PR is part of the migration of materials from eth.wiki to ethereum.org. There is substantial material on eth.wiki concerning proof of stake that was not available at ethereum.org and should not be lost when the wiki is deprecated. The PoS page currently on ethereum.org is also rather sparse and makes frequent reference to sharding designs that have since been deprecated. For these reasons I have reworked the PoS landing page with up-to-date information and also added two new subpages: one on weak subjectivity and another explaining the Gasper protocol. This satisfies the migration of PoS materials from eth.wiki. Note, however, that the material there was written when Casper was the cutting edge of PoS research, meaning it lags significantly behind the mechanism that will be implemented at the merge. Therefore, I have rewritten and updated where necessary.

In summary the following changes are implemented:

• Substantial rewriting of PoS landing page, includign removal of OOD information
• Add new "Gasper" page that cointains high-level explanation of Casper and LMD-GHOST as they will be implemented at the merge
• Add "weak subjectivity" page. This is part of the wiki migration but content rewritten to better fit ethereum.org

Note also that, contrary to the suggestions in the wiki migration issue I decided NOT to migrate the PoS FAQs onto ethereum.org. This is because they are already replicated verbatim on vitalik.ca. I have simply linked out to that page instead.

Related Issue

#5690

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[minimalsm]

Could we use proof-of-work / proof-of-stake over the acronym as per the style guide

[jmcook1186]

done

[minimalsm]

Hmmm I had to fix a bunch of these and realised that this maybe isn't actually clear:

We stick to spelling out full terms (proof-of-stake) over acronyms (PoS) to avoid the potential cognitive overhead it causes.

See this section of the Google Technical Writing Guide for the reasoning we used to inform this choice.

[minimalsm]

Hey @jmcook1186, this looks great ❤️❤️. Left some high-level comments but will try to do a full review by tomorrow.

[minimalsm]

Suggested change

	description: An explanation of the Gasper PoS mechanism.
	description: An explanation of the Gasper proof-of-stake mechanism.

[minimalsm]

This is great @jmcook1186 (And I actually learned a bunch, thanks 😀)! I've committed some formatting changes but nothing major.

Left two comments for you to consider but not blocking this PR; we can definitely merge this and work on those later.

I also think we want to consider where we want these to live as they seem a little bit beyond 'Foundational' (definitely not something to worry about just now, we can do this at a later date).

[wackerow]

@jmcook1186 This is great! Love to see the expansion of these resources within the repo.
Left a few small comments/suggestions/questions, but overall think this is great and looking forward to pulling it in!

[minimalsm]

Just waiting on another review before merging.

[samajammin]

FYI having incomplete: false, while more explicit, isn't necessary. We can just remove this frontmatter prop ✂️

We only need to add incomplete: true if we want to display the incomplete banner & callouts on a docs page.

[wackerow]

💪🏻