SDK Release Notes don't link forward

Raising this as a blocker as:

• I think the potential impact is very high, for a long time we've had a stable URL for release notes. This URL is still valid but stale, meaning that people could go for a long time without hearing about new releases and fixes.
• This has blocked an internal process.

Happy to discuss the priority though.

This has come up before (e.g. DOC-1523), but the old release note page (https://developer.couchbase.com/server/other-products/release-notes-archives/php-sdk) does not mention it has been superseded by https://docs.couchbase.com/php-sdk/2.6/relnotes-php-sdk.html - as such, there's no way to know that you're looking at an incomplete page.

We should either maintain both pages, remove or redirect the old one, or have the old one explicitly mention at the top that it is no longer correct and you should check the new one.