Run prettier over markdown

[dannymidnight]

Following on from #2652 I thought it might be nice to run Prettier over all the files to adjust indentation in one big bang.

Turns out there's an outstanding issue in Prettier that needs to be resolved before we can drop this in otherwise we keep some extra indentation.

• Tab width should not affect text alignment after the bullet points in Markdown lists prettier/prettier#5019
• Removed excessive spaces after line prefixes for unordered lists in Markdown prettier/prettier#15526

[buildkite-docs-bot]

Preview URL: https://2654--bk-docs-preview.netlify.app

[gilesgas]

Thanks @dannymidnight for the catch-up to better explain the purpose behind this PR.

While I haven't had the chance to switch across to Prettier as an IDE plugin (to assist with developing content for the Buildkite Docs yet), I've tweaked the existing plugin I use (Markdown All in One) to check my syntax before submitting updates - in particular, the my IDE now points out additional spaces at the ends of lines.

A couple of things to note about contributing to these Markdown docs which might be considered different from practices employed when contributing to Markdown files more closely associated with actual code (e.g. READMEs):

• When implementing numbered lists, each numbered list item should begin with just 1. (and not be numbered sequentially). Numbering sequentially results in the need to re-number downstream list items (when additional steps need to be inserted part-way through), and also impairs the ability to review actual changes in PR diffs - i.e. every downstream list item from the inserted list item would indicate unnecessary changes too.
• For bulleted lists, we don't want any additional spaces added between the bullet list indicator (e.g. -) and the text that follows. This impairs the readability of the source. I'm not sure if this is (still) a Prettier bug or this can be tweaked in the UI.

At some point in the near future, I'd like to prepare a proper 'contributors guide', which would provide instructions on how to configure an IDE plugin (like Prettier or Markdown All in One) to check/reformat the docs such that they'd build correctly once pushed up.