Version 1 EOL followup

[chalin]

Requirement

From #1054 (comment):

@yurishkuro, after giving this more thought, I'd like to argue that the most appropriate action for end users is to:

• Keep 1.76 pages indefinitely
• Redirect 1.x pages to the corresponding 1.76 page, assuming it exists, or to the 1.76 landing page otherwise.

Why?

1. URLs are like public APIs. There are lots of URLs to 1.x pages out there (blogs, runbooks, tickets, vendor docs, PDFs, bookmarks including OTel.io blog posts). Simply deleting them is a serious breaking change that just leaves clients confused and unaware of any suggested migration path.
2. By keeping 1.76 pages, we can clearly mark v1 as EOL and funnel users to v2. That is, add a banner to 1.76 pages + links to migration + 2.x equivalents so that users are informed, not surprised.
3. Redirecting 1.x → latest 2.x silently changes semantics. You propose redirecting to 2.x pages, but users following an old link expect 1.x behavior. Landing on 2.x can give wrong flags, configs, or deployment instructions — a correctness bug, not just UX.
4. Keeping 1.76 pages has a very low support burden.

Tasks

• Redirect 1.x pages to corresponding 1.76 page if it exists, otherwise to the 1.76 landing page - Add edge function to handle v1 page redirects, and other adjustments #1056
• ...

As specified by @yurishkuro in #1054:

• Add banner to 1.76 pages. See Download page example below.
• Drop "latest) from "1.76 (latest)" since it's misleading

Reference, examples:

on Download page we have a warning