Rework semconv-spec-version scripts so version can be used in schema/latest redirect

[chalin]

As noted in #3475, there's a simpler way to implement this feature:

• Fixes Is there an index for all available schema? #3256
• (Was formerly a part of Schemas: add index page #3469)

Redirect test: https://deploy-preview-3475--opentelemetry.netlify.app/schemas/latest

$ curl -sI https://deploy-preview-3475--opentelemetry.netlify.app/schemas/latest | grep -E 'HTTP|loc'
HTTP/2 301 
location: /schemas/1.22.0

Note: there's a simpler way to get the latest version, by using the semconv spec version. But to do that I'll need to rework some scripts. I'll do that in a followup PR.

Creating this issue to track the followup work.