List available schemas in 404 response to /schemas

[chalin]

• Fixes /schemas is the top 404 #3468 by adding an index page, if semconv and spec folks agree to this feature.
  Note that the list is autogenerated from content-modules/semantic-conventions/schemas
• Fixes Is there an index for all available schema? #3256 moved to Redirect /schemas/latest to latest schema #3475
• Fixes Ensure that schema files are served with content-type application/yaml #3416 moved to Schema content-type fix #3474

---

Preview: https://deploy-preview-3469--opentelemetry.netlify.app/schemas/

Screenshot (mobile)

[chalin]

/cc https://github.com/orgs/open-telemetry/teams/specs-semconv-maintainers @jsuereth @tigrannajaryan

[tigrannajaryan]

I think it is a good idea to point /schemas/latest to the latest published schema.

I don't think we should publish a human-readable list at /schemas/. My previous argument still holds: if we want /schemas/ to contain anything it should be a machine-readable format defined in Otel spec. Since we don't have such format defined I think we should not publish anything at the index yet.

[chalin]

Thanks for your response @tigrannajaryan - see #3468 (comment) for a clarification of the current situation (/schemas/ already returns human readable HTML) and two suggested ways for us to have our cake and eat it too 🎂 😄.

[chalin]

Converting to draft until we reach a consensus at #3468.

In the meantime, I'm testing the option of returning a 404 status for the schema index page, while still providing the list of schemas in human readable form.

[chalin]

Ok, I'm going to split this up so as to not hold back the individual fixes. Here's the first:

• Schema content-type fix #3474

[chalin]

Here's the other feature factored out:

• Redirect /schemas/latest to latest schema #3475

I'll repurpose this PR to be only about the index page.

[chalin]

Closing in favor of:

• Add /schemas in YAML, /schemas/list in HTML, and a 404 page for the rest #3537