Update "Learn how to use Fleet" for Fleet Sandbox (#7142)

- Update "Learn how to use Fleet" docs page to walk a Fleet Sandbox user through adding their device and running a query
- Add a "Get operating system information" query to standard query library for the "Learn how to use Fleet" walkthrough
- Update Fleet's top level README to point users who want to try Fleet to Fleet Sandbox
- Update "How to install osquery..." (macOS, Windows, Linux) blog posts to point users who want to try Fleet to Fleet Sandbox
- Move `fleetctl preview` questions to "Contributing" FAQ section in docs. This is because `fleetctl preview` is now a testing tool for Fleet contributors
- Update "Deploying" docs to point users who want to try Fleet to Fleet Sandbox

.github/ISSUE_TEMPLATE/smoke-tests.md

@@ -15,7 +15,7 @@ assignees: ''
 
 # Important reference data
 
-1. [fleetctl preview setup](https://fleetdm.com/get-started)
+1. [fleetctl preview setup](https://fleetdm.com/fleetctl-preview)
 2. [permissions documentation](https://fleetdm.com/docs/using-fleet/permissions) 
 3. premium tests require license key (needs renewal) `fleetctl preview --license-key=eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJGbGVldCBEZXZpY2UgTWFuYWdlbWVudCBJbmMuIiwiZXhwIjoxNjQwOTk1MjAwLCJzdWIiOiJkZXZlbG9wbWVudCIsImRldmljZXMiOjEwMCwibm90ZSI6ImZvciBkZXZlbG9wbWVudCBvbmx5IiwidGllciI6ImJhc2ljIiwiaWF0IjoxNjIyNDI2NTg2fQ.WmZ0kG4seW3IrNvULCHUPBSfFdqj38A_eiXdV_DFunMHechjHbkwtfkf1J6JQJoDyqn8raXpgbdhafDwv3rmDw`
 4. premium tests require license key (active - Expires Sunday, January 1, 2023 12:00:00 AM) `fleetctl preview --license-key=eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJGbGVldCBEZXZpY2UgTWFuYWdlbWVudCBJbmMuIiwiZXhwIjoxNjcyNTMxMjAwLCJzdWIiOiJGbGVldCBEZXZpY2UgTWFuYWdlbWVudCIsImRldmljZXMiOjEwMCwibm90ZSI6ImZvciBkZXZlbG9wbWVudCBvbmx5IiwidGllciI6InByZW1pdW0iLCJpYXQiOjE2NDI1MjIxODF9.EGHQjIzM73YyMbnCruswzg360DEYCsDi9uz48YcDwQHq90BabGT5PIXRiculw79emGj5sk2aKgccTd2hU5J7Jw`