Add dust concentration diagnostics

### Are there any linked Issues or Pull Requests?

_No response_

### Brief description

Diagnostics equivalent to STASH codes: 17257, 20058 and 20059 are required.

These could be based on a concentration diagnostic:

(aerosol__acc_ins_du + aerosol__cor_ins_du) * rho_in_wth

OR:

(aerosol__acc_ins_du + aerosol__cor_ins_du) * 1000000000 * rho_in_wth

These could be zoomed to levels, meaned over levels etc. to produce the desired diagnostics in XIOS.

This fails - probably with underfow error (XIOS and the PET0000.lfric_atm.Log error messages give no details, it just stops). That's a separate issue, but for now these diagnostics need to be created in-model.

### Further details of the issue.

_No response_

Start by tracing the existing in-model diagnostic path for STASH codes 17257, 20058 and 20059, and compare it with the proposed total_dust_concentration expression. Check how XIOS level selection and averaging are currently handled, then confirm that the three dust concentration diagnostics are produced in-model without the reported XIOS failure.

Written by the indexing model from the issue text.