Add stats for prod121

[dominikl]

See title. Just have to put the release date in once we've finally decided.

Just to double check, the actions in IDR/idr-metadata#691 won't change the stats for idr0070, would they @will-moore ?

[will-moore]

@dominikl I think the stats will be affected by that PR (different image counts), but it won't be included until the NGFF release (prod122?)

[dominikl]

Ah yes of course. True, the number of images, size, etc will be different. Ok, have to remind myself to update idr0070 stats for prod122 release.

[will-moore]

Also prod122 will include the deletion of a duplicate plate for idr0015 (see IDR/idr-metadata#675 checklist)