Revises IA of the getting started section

[benironside]

This PR fixes issue 23 in our docs projects repo. Updates the ESS docs Getting Started section for 8.14 and 8.15.

• Moves some requirements pages to the sections about their corresponding features (not all reqs pages were moved, I didn't make the new section for Defend yet)
• Moves the Elastic Security UI page into the Getting Started section
• Other minor revisions to the Getting Started

Note: This PR affects organization only. It does not make content updates.

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[nastasha-solomon]

Thank you for re-orging this! It looks great 👍🏼 Just left two suggestions for your consideration.

[natasha-moore-elastic]

One suggestion about EA, otherwise looks great! 🚀

[joepeeples]

LGTM! Though I was expecting a bit more of an overhaul, esp compared to the outlines in the originating issue and the Google doc, with new "Get started" subsections for each product area (SIEM, Endpoint, Cloud). I assume that'll come in later iterations, and this PR is just the start of the reorg.

Also, maybe a bit out of scope, but we should standardize whether we call things "requirements" or "prerequisites" (or both!), in topic titles and anywhere else. The difference between terms is pretty nuanced and probably lost on most users, so we should just pick one and stick with it. Nothing that needs to go into this PR; we can do that later when we're focusing more on content and not just organization.

[jmikell821]

Thanks! Left a comment. Also - does this PR move the feature-specific reqs to their respective sections? Or are we doing that in phase 1B?

[jmikell821]

I would put ingest after Elastic Endgame reqs, closer to the top. Here's the proposed order according to our doc but I'm open to suggestions.

[benironside]

"does this PR move the feature-specific reqs to their respective sections?" - Yes, the only exception being the Elastic Defend stuff since we haven't made a section for it yet.

[nastasha-solomon]

lgtm - thank you for reorging this!