[DOCS] Salt should make use of canonical URLs or `noindex` presence within non-latest or non-master HTML documentation

Description

When users use a search engine to find the appropriate Salt documentation, multiple results can appear for the same page across multiple Salt versions. This makes search have multiple results, causing search to be more difficult to use when multiple results are the same page (just with a different version label).

Suggested Fix

In the publishing of documentation, we publish multiple versions. This means we should either have latest or master published docs be the canonical URLs, and have all the other versions of documentation use metadata to point to the appropriate canonical URL endpoints.

This will help with SEO, and will help reduce the search results seen in search engines.

That, and to also verify/confirm that robots.txt is also blocking out. According to robots.txt, the docs would still appear in Google searches.

An alternative would be to simply add the noindex value into metadata on all non-master or non-latest documentation (depending on which is meant to be the prime documentation to reference).

Type of documentation

HTML Salt documentation

Start by reviewing how the published HTML Salt documentation is generated across versions and inspect the current robots.txt behavior. Determine whether latest or master is the primary documentation, then define and verify the canonical URL or noindex metadata for other versions. Done means duplicate versioned pages are handled as intended and search-engine indexing behavior is confirmed.