Compress ANY large payloads when saving, not just `Cube.data`

[trexfeathers]

✨ Feature Request

Compress ANY large payloads when saving, not just Cube.data.

For example an ancillary variable with the same dimensionality as the Cube could be very large, but often only has a few discrete values.

Motivation

Reported by @pasc85. Saving a status flag - which can either be 0 or 1 - is producing an unnecessarily large file. this is an obvious case for compression since the array will have a large shape, but could in theory be represented using a single bit

Additional context

• I don't know if this can easily extend to all file types or should just be limited to NetCDF as in the original use case.
• @bjlittle's initial idea is to automatically apply compression to anything with the same shape as Cube.data.