docs: add docs for editorconfig to configuration and options

[midgleyc]

Description

Add documentation for editorconfig to the "options" and "configuration" sections.

#2760 initially added a paragraph to configuration, but this was reverted in #3213, and the reintroduction in #3255 only added to the "API" and "CLI" sections.

This change copies the paragraph from API's resolveConfig to the bottom of "configuration", and adds sentences to the relevant parts of "options" to increase discoverability of this feature.

Fixes #8044.

Checklist

• I’ve added tests to confirm my change works.
• (If changing the API or CLI) I’ve documented the changes I’ve made (in the docs/ directory).
• (If the change is user-facing) I’ve added my changes to changelog_unreleased/*/XXXX.md file following changelog_unreleased/TEMPLATE.md.
• I’ve read the contributing guidelines.

✨Try the playground for this PR✨

[fisker]

@sosukesuzuki I guess we are going to make a patch release soon? If not, we may want copy these lines to the website.

[sosukesuzuki]

@fisker I will release new patch version soon. (for #11892)