Add "before" and "after" date parameters

[dlh01]

Description

It isn't possible to pass a date query via a flag argument (see also wp-cli/wp-cli#4616), but we could accept --start-date and --end-date flags that map to a date query.

Use Case

We were once asked to provide an audit for posts published in the last 12 months. We had to settle for two year-based queries.

[Eniamza]

Hey, Can you provide a sample command for this specific use case? I'm also struggling with the same issue.