Additional metadata to understand "usability" of a card

[codingcyclist]

Hi there,

I'm a big fan of dbt-metabase! Especially the exposures feature has been a complete game changer to avoid deploying model changes that would break metabase cards.

With a growing number of cards in Metabase, my team figured that it's not only important to understand by which cards our DBT models are referenced , but also whether these cards are still being used. Hence, I was thinking to add the last_used_at and average_query_time fields from the metabase card API to the exposure metadata. They strike me as a good proxy for whether a card is still usable (query time) and whether it gets used (last used timestamp)

I've already done this on a local fork (see screenshot) of the repo and would be happy to contribute it. Wdyt @gouline?