Add missing `_nicontains` filter operator

[joselcvarela]

[vercel[bot]]

@joselcvarela is attempting to deploy a commit to the Directus Team on Vercel.

A member of the Team first needs to authorize it.

[phazonoverload]

I'm pretty sure this was purposefully undocumented because it is not consistently available in all places that filters should be.

It was originally a drive-by PR that probably should not have been merged

Does this ring a bell @rijkvanzanten?