SC-14561 add fleet and discovery

[cpipilas]

Integrate our new Fleet and Discovery in our docs.

Added / Changed:

• New Fleet and Discovery section. Subsections:
  • Overview - New page with info/links about both Fleet, Service and Logs Discovery
  • Fleet - Updated
• Under Monitoring, Autodiscovery page renamed to Service Discovery and content updated
• Under Logs, Discovery section updated
• Agents > Sematext Agent > Autodiscovery page renamed to Service Discovery a new Overview page added
• New Fleet & Discovery tile in docs Getting Started page

[otisg]

@cpipilas Haven't looked at the actual content yet, just scanned the TOC to see what was changed/added and one thing I wondered about is whether it makes sense to have "Fleet & Discovery" as a separate top-level thing, while at the same time we have Monitoring > Autodiscovery and Logs > Discovery. Btw. are we doing to update those? Content or screenshots or both? Maybe once we start doing that we'll see how to unify things...

Thinking about this very briefly now...thinking about this now out loud... I also wondered if F&D should go inside User Guide given that it feels like a platform sort of functionality. But then again we have things like Alerts, Events, Dashboards, and Teams, all of which are also platform-level things, but we exposed them at top-level for visibility.

Order-wise... Should F&D come after user Guide since F&D is what people see first when they join? Should Team come after F&D because inviting is often done early during onboarding?