Update testnet documentation

[ardislu]

This PR updates documentation relating to Ethereum's public testnets, especially regarding the Goerli testnet which has been deprecated for over 2 years now.

Description

• Replace Goerli with Hoodi
• Update or remove broken links
• Remove language describing the testnets as newer/older, larger/smaller in size, more/fewer dapps deployed, etc. These facts will change over time, and are therefore more likely to be misleading than useful.

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[github-actions]

This issue is stale because it has been open 30 days with no activity.

[ardislu]

Hi, can this PR get untagged as stale? I just rebased my commit to the tip of dev, the changes are still valid.

Goerli has now been deprecated for over 2 years.

[ardislu]

Rebased and updated for Hoodi. Now the currently live documentation about Goerli is 2 testnets behind and really outdated.

[corwintines]

Thanks @ardislu this is great!

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