lenient intersetion_of_cubes()

[bblay]

✨ Feature Request

An LFRic eastward wind cube has a pressure coord with slightly more metadata than the UM one (see attached image). This causes _dimensional_metadata_comparison(), and therefore intersection_of_cubes(), to incorrectly think the coords different.

I can work around this but wanted to suggest that this could be improved by allowing intersection_of_cubes() to be lenient.

A quote from a scientist, as a second opinion: "...one feature of Iris that bugs me a bit is how fussy it is with the meta data needing to be exactly the same".