Added a cache version number, to reset cache as needed (#1334)
Added a cache version number, to reset cache as needed (#1334)

* Added a cache version number, to reset cache as needed

* Altered comment

Co-authored-by: Chris Sampson <c98214dce9798115caa9d69ad6a57408aaf4a51f@metoffice.gov.uk>
metoppv/improver,fionaRust/improver,fionaRust/improver,metoppv/improver