Look into Prettier formatting for code samples

[alexandratran]

Look into using Prettier for formatting the code samples in all Markdown files. May have to use a specific configuration to not lose certain Markdown formats we use (e.g., line breaks at a certain column limit). See the code guidelines used in https://github.com/MetaMask/metamask-docs/pull/1116.

Edit: We want to revert back to 2 space indents instead of 4 across the docs.

Edit 2: Installing eslint-plugin-markdown is blocked by requiring Node v18+. We need to update Docusaurus first (#1048).

[subhamkumarr]

@alexandratran For snap and wallet, code formatting is already done. For the Service section and a few other markdown files, shall I do the code formatting?