[Discover] Add links to documentation for Document Explorer

[shaunmcgough]

Advertise the new features in Discover: Document Explorer, Field Statistics, and Alerting. This will occur across three releases and requires the following input from dev, docs, design, and PM.

8.1.x

• Add a "Learn more" link to the Document Explorer setting on the Advanced Settings page. The link should use the docs link service and point to the Document Explorer page. .

• Add a "Learn more" link to this Discover callout. Note: the link should not be the primary call to action.
  The following screenshot is from the security landing page. Note the primary call to action and the link to the right which says, 'Dismiss message'. If the Docs link 'Learn more' was like the 'Dismiss message' it would satisfy the product requirement.

8.2.0

• Rewrite the callout to say something along the lines of "We made documentation exploration easier" and link to the Document Explorer doc and video.
• Ensure content for Document Explorer, Field Statistics, and Alerting is updated in the docs.
• Create a new Marketing page that advertises the three new features of Discover: Document Explorer, Field Statistics, and Alerting.

8.3.0

• Add a product tour of the Document Explorer based on this prototype. The tour is dependent upon this feature request.

@andreadelrio for design guidance if needed, @gchaps for docs, @adeline-tan for marketing page

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[rayafratkina]

In discussion today we decided this should be a blocker for 8.2 - we need to communicate the change to users explicitly

[VijayDoshi]

Changes that need to be communicated are referenced in the Document Explorer and Video link above. Getting a link to that and a compelling call to action in the banner is important.

Secondarily, we should have callouts for Alerting in Discover as well as Field Statistics Tech Previews.

I think all of this can go in the same banner, with the primary CTA to Learn what's new in Discover (unless someone else has better language).

@adeline-tan From a marketing POV I think we would benefit from a landing page where we can bring these three features together at a higher level.

[gchaps]

@VijayDoshi: Here is a callout that @andreadelrio and I worked on for 8.2:

[gchaps]

Another suggestion for the title is "Exploring your data just got easier"

[VijayDoshi]

@gchaps Looks good to me.

[gchaps]

Here's the final text:

Exploring your data just got easier
Experience the new Document Explorer. Understand your data with Field Statistics. Take action on your search results with Alerts.

[kertal]

Closing this since we reached 8.3 ... and we delivered #131125