Support Diagnostic v8.4.0

This release increments the minor (8.3 to 8.4) because of the /_cat/nodes change, which tweaks the columns in a simple script-breaking way (both order and the selected columns).

What's Changed

• Update CAT Node Headers by @stefnestor in #591
• [ES] Add GET /_internal/_health by @pickypg in #593

Full Changelog: v8.3.0...v8.4.0