[DOCS] Link to `current release document` should point to current page in the current docs, when possible.

[wasserman]

I consider some of this unexpected behavior a bug, but I've added some improvement suggestions that could be a feature.

Description of the problem including expected versus actual behavior:
Often I find docs via a Google search. The top result doesn't often land on the current version of Elastic. The banner that appears on top of the doc page suggests to go to the current release document. Unfortunately this often redirects the main index of the docs. Then I have to find the corresponding page via the index or go back to the original landing page and flip the version on the side drop-down or edit the url accordingly. I'd expect this link to send me to the same doc in the current version and if no longer valid go to the index of the page. Ideally, if it is no longer valid, it could include a deprecated message in the banner since going to the current docs would be misleading without at least a warning.

Steps to reproduce:

1. Go to a document page that isn't the current version, such as https://www.elastic.co/guide/en/elasticsearch/reference/6.x/geoip-processor.html
2. Observe the notification banner suggesting to go to the current release document.
3. Click current release document link.
4. Notice you get sent to https://www.elastic.co/guide/en/elasticsearch/reference/current/index.html

Workaround scenario:

1. Go to a document page that isn't the current version, such as https://www.elastic.co/guide/en/elasticsearch/reference/6.x/geoip-processor.html
2. Select Elasticsearch Guide drop-down and select 7.12 (current), or whatever version is current at the time you look at this.

[elasticmachine]

Pinging @elastic/es-docs (Team:Docs)

[jrodewig]

Thanks for submitting this @wasserman. I'm going to transfer this to our elastic/docs repo as this is related to our docs system rather than the Elasticsearch docs content.

As a note, we're currently working on revamping our docs experience to fix flows like this.

[gtback]

Thanks for reporting this, @wasserman ! It's actually the same issue as #1743, but because the title of this is more accurate and the description gives more context, I'll actually leave this one open and close the older one. Some relevent comments:

From @debadair:

The banners are standard boilerplate that's inserted automatically on each page by the doc build. The "current release documentation" link is relative to the book, but is not "page aware".

The version picker is page aware and enables users to flip to the same page in the current version, if it exists.

Depending on how we handle this messaging in the new design, we could either make the links page aware, or remove them and direct the reader to switch versions using the standard mechanism. (Redundant navigation elements aren't necessarily a desirable thing...)

From me:

Each version of each book (for example, the 7.5 Elasticsearch Reference and the 7.6 Elasticsearch Reference) are built independently, so there's currently no way for one page to know that the other versions have an equivalent page, at build time. The version dropdown is smart enough to figure out when the equivalent page exists or not, so it should be pretty straightforward to make the banner at the top do the same thing.

[gtback]

As @jrodewig mentioned, we're working on completely replacing the docs system, and we may not fix this in the current system, but we'll definitely keep it in mind for building the new one. Thanks again @wasserman !