Update opportunistic caching page to remove experimental warning (#6926)
Update opportunistic caching page to remove experimental warning (#6926)

Opportunistic caching is no longer considered experimental as it's
five years old.

Co-authored-by: Timothee Chehab <23862619428d0e01b78fbf12f6547dd494c966f5@symaps.io>
blaze/dask,jakirkham/dask,dask/dask,blaze/dask,dask/dask,jakirkham/dask