Edit get-started/install page

[LarryUllman]

This cleans up the get-started/install page

• change title to "Install"
• page doesn't discuss configuration so I removed that text
• DB content goes on the self-hosted page (makes this page simpler and encourages "just use Cloud")
• remove esoteric content
• make the TOC cleaner and better targeted
• point to quickstart after this instead of the tutorial

I also removed the instructions for how to install SQLite entirely because:

• As mentioned in the text, SQLite is already commonly installed
• That information isn't specific to Prefect
• That information is already--and better--found elsewhere online

Checklist

• This pull request includes a label categorizing the change e.g. maintenance, fix, feature, enhancement, docs.

For documentation changes:

• This pull request includes redirect settings in mint.json for files that are removed or renamed.

[discdiver]

Nice changes to simplify! Minor nits.

[billpalombi]

lgtm