Add Network Topology plugin docs

[mdbirnstiehl]

Description

This PR closes https://github.com/elastic/docs-content-internal/issues/1147 and adds

Three new pages for the Network Topology plugin (technical preview, self-managed 8.19 only): an overview landing page, a setup tutorial, and a field reference.

Remaining tasks:

• Screenshots for step 5.
• Potential troubleshooting updates for common logstash SNMP input errors.
• Architecture diagram for the landing page.

Documentation sets edited in this PR

Check all that apply.

• Stateful (docs/en/observability/*)
• Serverless (docs/en/serverless/*)
• Integrations Developer Guide (docs/en/integrations/*)
• None of the above

Related issue

Closes https://github.com/elastic/docs-content-internal/issues/1147

[github-actions]

🤖 GitHub comments

Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)

[benironside]

Very cool, highly technical, good work! I gave a pretty thorough review, for someone who didn't know most of the acronyms involved. Left a few minor prose suggestions.

A few other suggestions:

• Add requirments/RBAC info
• Maybe link to some info about ILM? Feels like a natural next step to me since you've just figured out how to pull in a bunch of data.
• Consider adding the "location" fields to the tutorial so people know how to get their data associated with the right site.

Finally, for today's NIT OF THE DAY that I think might actually nudge the needle...
On the reference page, what do you think of making the "Example" columns into "Examples" or even "Example(s)"?

Since some of the example values are multiple examples, this would marginally help make clear that for e.g. "host.type", you can't have a value of e.g. "router, switch", but rather "router", or "switch". Perhaps this is already obvious, after all, I figured it out. But if we pluralize, nobody else will ever have to.