Improve the adding hosts section of the docs

[DominusKelvin]

Goal

TODO

Based on the research, studies, and learning from #3931, this improvement is an initial project to apply those learnings on a tangible page(in this case, the adding hosts 'page)

How?

• Deduplicate the page as much as possible by cutting back on words and linking to other sections of the docs when necessary.
• Clearly showing that Fleet both support plain osquery as well as other agents but recommended for a better experience, orbit should be used.
• Link to the FAQ regarding adding hosts at the end of the page.
• Cleary show the happy path of adding hosts to a Fleet instance

[DominusKelvin]

cc: @noahtalerman

[noahtalerman]

@DominusKelvin looks great!

[DominusKelvin]

Thanks @noahtalerman

[noahtalerman]

@DominusKelvin heads up, I'm re-opening this issue and adding it to the "In progress column" in the #g-community board.

It looks like the PR associated with this issue hasn't been merged: #5615