Plugin to set track numbers

### Use case

I'm trying to use Beets to autonumber tracks in a folder or in a query according to the sort order. I acquainted my self with the documentation for Beets and was unable to find a similar feature. Mp3tag (windows only), my tagger of choice, is able to do this:

Kid3 (GUI & CLI) is able to do this as well:

### Solution

I'm sure Beets devs wouldn't have any problem thinking of how to implement this, but if they want a proposal from me, I'd say to provide a command like `beet autonumber [FirstTrackNumber] QUERY [SortOrder]`.

So that if there are just three tracks in the path `~/youtube-dl/bunch-of-unreleased-poorly-tagged-soundcloud-music/`, with artist tags Aphex Twin, Tame Impala, and Fleet Foxes respectively, running this line:
`beet autonumber 1 'path=~/youtube-dl/bunch-of-unreleased-poorly-tagged-soundcloud-music/' artist+`
would set the tracknumber to 1 for the Aphex Twin track
tracknumber 2 for the Fleet Foxes track
tracknumber 3 for the Tame Impala track

### Alternatives

I couldn't find a plugin that does this in the Beets docs.