migrate info on pow-mining from ethdocs and eth.wiki

[jmcook1186]

Description

This PR aims to migrate information from the ethdocs.org and eth.wiki sites to appropriate pages on ethereum.org so that the information is preserved when those websites are deprecated.

To this end, I have done the following:

1. Added some introductory material to the existing pow mining page
2. Added a brief high-level paragraph on mining algorithms to the existing pow-mining page
3. Added a new directory, /mining-algorithms, beneath /consensus-mechanisms/pow
4. Added a landing page and two subdirectories to /mining-algorithms: /dagger-hashamoto and ethash
5. Migrate info from ethdocs and eth.wiki pages on mining algorithms into dagger-hashamoto/index.md and ethhash/index.md
6. Update menus and links to make new pages visible.

Related Issue

This resolves suggested PR 12 from #5690 and PR 3 from #5731

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[minimalsm]

Looking great! Found it very well put together and educational for me.

Comments are mostly around site conventions or some simplifications I think we could make, but I'll leave those up to you.

[wackerow]

@jmcook1186 🙏🏻 Thank you again for these. Great addition to fill out the background of PoW, appreciate your work on this. This seems super close.. bunch of code suggestions left, mostly non-controversial I feel.

Let me know if you want a hand tuning this up, we'll try to get this in soon =)

[wackerow]

💪🏻 Thanks again @jmcook1186!

[minimalsm]

LGTM :) Pushed some commits to add further reading section to each page. Merging now 🚀

Some low priority things we should tidy up at some point:

• Memory hard - should we explain what this means? (I’ve added a link out to wikipedia for now)
• Appendix - We should link to appendix using footnotes (see NFT page for example of this on site)
• EthHash page needs prerequisites
• UI bug introduced in our developer docs sidenav by the depth (I will create an issue)

Dagger Hashamoto page

“## More efficient cache-based evaluation algorithm {#cache-based-evaluation}” section

• Providing a sentence for context here would be good