docs/integrations: a single-page intro to tech CUE integrates with

[jpluscplusm]

Turn the existing content-less URL into a high-level, tickbox, "yes, CUE works with X" for folks wanting to sense check if they can make use of CUE.

This page:

• pull in any content from its subpages, as needed
  • don't replicate any "XYZ is planned" language
  • make sure that an issue/roadmap-entry/etc exists, as appropriate, tracking the aim
• include language-specific pointers to other (possibly new/moved) docs
  • e.g. so that a Go user can see a compact list of CUE capabilities
    • with links pointing to a more complete search/tag page
• don't include any technical content or examples on the page, unless they're very short.
  • this should primarily be links to other docs
• remove/migrate all sub-pages, in line with the points below
• language:
  • don't use the word ""integration"", as it implies there's a tangible "thing", which makes it harder to differentiate "integrations" (which aren't tangible) from "adapters" (which are/will-be tangible, usable things)
  • use the phrase "integrates with" on this page to point to specific capabilities (e.g. JSON/YAML)

Subpages:

Adapt and reword subpages' content into new, newcomer-friendly concept guides.

Migrate most of the "JSON" and "YAML" content to concept/{json,yaml} as appropriate. And/or docs/tour (when it's showing off a feature) or docs/introduction (when we want to make sure the reader knows that a core capability exists)

Change the page's current URL of /docs/integration/ to /docs/integrations/, plural.

[jpluscplusm]

https://cuelang.org/cl/1192707

[jpluscplusm]

Current status of CL (https://cuelang.org/cl/1183402 (has comments) superseded by https://cuelang.org/cl/1192707): blocked on #72 & #75.

[jpluscplusm]

Previous CL: https://cuelang.org/cl/1183402 (has comments) Current CL: https://cuelang.org/cl/1192707 (supersedes previous)