add handling of `filter_dicoms` to parallel `filter_files` and deprecated `filter_dicom`

[yarikoptic]

Inspired by @mslw 's

• DOC: fix the description of filter_files #823

Let's add filter_dicoms handling in heuristics which would be expected to return True for those which to keep, that would make it consistent with filter_files

• in logic
• in naming (plural)

and then announce filter_dicom deprecated (DeprecationWarning) with removal some time in the future.