[Ruleset Engine] Add two new fields to the reference

[pedrosousa]

Summary

Addresses PCX-20454.
Also adds the correct edit link for "Fields reference" pages (main page and sub-pages).

Documentation checklist

• The change adheres to the documentation style guide.

[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
*	@cloudflare/pcx-technical-writing
*.astro	@cloudflare/content-engineering, @kodster28

[github-actions]

Preview URL: https://ec499659.preview.developers.cloudflare.com
Preview Branch URL: https://pedro-pcx-20454-ruleset-engine-add-two-fields.preview.developers.cloudflare.com

[pedrosousa]

Preview URLs:

• New fields (notice that there are now edit links in these detail pages):
  • https://pedro-pcx-20454-ruleset-engine-add-two-fields.preview.developers.cloudflare.com/ruleset-engine/rules-language/fields/reference/cf.timings.edge_msec/
  • https://pedro-pcx-20454-ruleset-engine-add-two-fields.preview.developers.cloudflare.com/ruleset-engine/rules-language/fields/reference/cf.timings.origin_ttfb_msec/
• Landing page (now shows an "Edit Page" link at the end of the page):
  https://pedro-pcx-20454-ruleset-engine-add-two-fields.preview.developers.cloudflare.com/ruleset-engine/rules-language/fields/reference/