Implementation of metadata-based freshness

[mikealfare]

resolves #890

Problem

The current implementation of source freshness requires querying the data and requires the user provide a datetime field. This is slower and more expensive than it should be. It doesn't scale across multiple models. And some models do not have an appropriate datetime field.

Solution

Use source metadata where available.

Checklist

• [x] I have read the contributing guide and understand what's expected of me
• [ ] I have run this code in development and it appears to resolve the stated issue
• [ ] This PR includes tests, or tests are not required/relevant for this PR
• [x] This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[github-actions[bot]]

This PR has been marked as Stale because it has been open with no activity as of late. If you would like the PR to remain open, please comment on the PR or else it will be closed in 7 days.

[github-actions[bot]]

Although we are closing this PR as stale, it can still be reopened to continue development. Just add a comment to notify the maintainers.