Built-in aggregation recipes do not work for operational UKV/MORGEPSUK data from MASS

### Describe the bug
First noticed in #1968, when using any of the built-in recipes which use `aggregate.ensure_aggregatable_across_cases` on operational data pulled from MASS (.pp format), it fails with error

> "Cube should have 'forecast_period' and 'forecast_reference_time' dimension coordinates."

This is as a result of `read.read_cubes` not loading these dimension coordinates when loading in the cubes.

### How to reproduce
Either by workflow or command line running cset bake, choose an aggregation method which uses `ensure_aggregatable_across_cases` on archived MASS data.

### Expected behaviour
This isn't a case of missing metadata, the `forecast_period`, `forecast_reference_time` and `time` coordinates all exist in the data, but do not exist as dimension coordinates.
The RES is able to aggregate with this data, so it should be possible in CSET too.