Add deprecation warnings for renamed commands

[kwigley]

Describe the feature

In #3554, we renamed source snapshot-freshness -> source freshness. Both commands are supported and no deprecation warning is showed. It would be ideal to show deprecation warnings when using the old command.

Describe alternatives you've considered

Support renamed commands forever via an alias and don't display any deprecation warnings. I'm perfectly happy with this answer as well, I'd happily close this issue if that is acceptable.

[jtcohen6]

I agree! Let's do both: continue support source snapshot-freshness as an alias forever*, and raise a deprecation warning when it's used.

*At least until dbt v2.0, if not longer :)

[github-actions]

This issue has been marked as Stale because it has been open for 180 days with no activity. If you would like the issue to remain open, please remove the stale label or comment on the issue, or it will be closed in 7 days.

[github-actions]

This issue has been marked as Stale because it has been open for 180 days with no activity. If you would like the issue to remain open, please remove the stale label or comment on the issue, or it will be closed in 7 days.

[github-actions]

Although we are closing this issue as stale, it's not gone forever. Issues can be reopened if there is renewed community interest; add a comment to notify the maintainers.