Improve titles in "Deployment models" section

[kilfoyle]

Feeback from Edu (via Slack) about the current Fleet Docs Information Architecture:

• It's a bit difficult to find where the Fleet Server installation guides are located, they are under "Deployment models", and in the past they were under "Set up Fleet Server" section.
• I like the deployment models section, but what do you think of renaming it a bit to Fleet Deployment Models or something like that?
• Also in the sub-sections the third one is missing Fleet Server, and the forth one has it. I think they should be aligned and keep names consistency (my vote is to include fleet server always, otherwise the users won't really know that it's the doc to install fleet server).