Update Guides for Tracked Built-ins

To advance [RFC #812 - Tracked Built-ins](https://rfcs.emberjs.com/id/0812-tracked-built-ins) to Recommended, we need to update existing documentation to make use of features the addon makes available, and guarantee the addon is well documented as well.

## Steps
- [ ] Go through the super-rentals tutorial for potential usages of `tracked-built-ins` and update where necessary.
- [ ] Go through guides-source for potential usages of `tracked-built-ins` and update where necessary.
- [ ] Expand "In-Depth Topics > Autotracking In-Depth" to missing data types cobered by `tracked-built-ins`
- [ ] ?