Migrate the legacy guide "Backpressuring in Streams" to the learn section

[bmuenzenmeyer]

Migrate the content currently at Backpressuring in Streams to a new page under the "learn" section found at https://github.com/nodejs/nodejs.org/tree/main/pages/en/learn.

• Use your judgement about what existing or new folder the content should go in. Ask in a draft PR if you are unsure.
• Review the content during migration, please do not simply copy/paste the content. Similar to Update how-to-read-environment-variables-from-nodejs.md with new .env guidance #6140, the content may need edits to account for the latest Node.js features.
• Add a redirect to the new content in redirects.json
• Run your content through a spell-checker in the editor, like https://github.com/streetsidesoftware/vscode-spell-checker, Word/Google Docs, Grammarly, or https://alexjs.com/

[NextThread]

Hey, can I work on this?

[AugustinMauroy]

@NextThread yeah gooo headed !

[NextThread]

#6261 raised my PR here

[paulobelucci]

Hi there! Here is my PR #6352 to review.