Add serverless links to solution cards in landing page

[dedemorton]

Adds a link to each solution card to direct serverless solution users to the correct docs.

You can view the preview here.

I'd like some feedback on the link text. I used generic text even though the links are specific because text like "View the Observability serverless docs" was quite long. I'd rather use text that's specific, if possible.

Closes elastic/observability-docs#3594

[github-actions]

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[dedemorton]

run docs-build

[dedemorton]

run docs-build

[dedemorton]

run docs-build

[dedemorton]

run docs-build

[dedemorton]

run docs-build rebuild

[KOTungseth]

LGTM. Let me know when you merge so I can track the metrics.

[bmorelli25]

@elasticmachine, run elasticsearch-ci/docs

[dedemorton]

@KOTungseth Before I merge this and make serverless more prominent on the docs landing page, I'm wondering if we should add some kind of statement to the serverless docs that describes the current availability of serverless.

The question underpinning this is: Will users who aren't involved in the preview be frustrated if they sign up for a trial and find out that they can't try out severless without getting waitlisted? There's nothing in the docs right now to let them know that they can't build serverless projects. There is this statement, but it's only on the main landing page for serverless and it requires users to read the blog to understand that they can't just build projects without getting access first:

"Elastic serverless products are currently in preview. Learn more about serverless in our blog."

Here's what users currently see when they look at the cloud console:

WDYT? Am I overthinking this?

[KOTungseth]

At the bottom of the blog, we say:

Become part of our serverless vision and try it out before everyone else — [apply now for early access](http://www.elastic.co/elasticsearch/serverless).

We could add a similar statement to the serverless docs landing page.

[dedemorton]

run docs-build