feature(filestore): add a hook to fix detected mimetype

Moves mimetype detection logic for Microsoft zipped formats from a file
plugin into a core plugin hook.
Adds missing reference to mime_type,file hook in the list of
available hooks.
Adds information about available hooks for filtering mime and simple types
to upgrading instructions. Informs plugin devs that Microsoft
zipped format detection snippet can be removed from file upload actions.
Merge pull request #7295 from hypeJunction/mimes_hook

chore(file): use a hook to fix detected mimetype