Clarify content around defer and source freshness checks

### Contributions

- [X] I have read the contribution docs, and understand what's expected of me.

### Link to the page on docs.getdbt.com requiring updates

issue: CSE Jenn Williams and a user flagged a point of confusion an enterprise user raised in a support ticket. the user couldn’t understand how to set up a job to run a model with freshness checks (fresher+) and also get the job to refer to the previous run state. They tried looking at the docs and mentioned the docs were limited in this so they reached out for help. i must say, i also found it a high effort to search for this.

Refer to [slack thread here](https://dbt-labs.slack.com/archives/C02NCQ9483C/p1698158135748019) for more context.

### What part(s) of the page would you like to see updated?

https://docs.getdbt.com/docs/deploy/source-freshness#checkbox

I’m wondering/suggesting whether we can add it to this page as a dedicated section. the loom is fab, but the UI is really outdated so if we want to use a video, it would need to be re-recorded.

### Additional information

_No response_