CMIP7 future scenario solar forcing for GA9 spectral files

[mo-jmanners]

Solar spectral variability is parametrised by adding time varying irradiances and Rayleigh coefficients for the spectral file sub-bands in an external configuration file (named as the spectral files with a _var extension).

This ticket will add ga9 spectral file configurations for the Future Solar Scenario as specified for CMIP7 here:
​​https://www.solarisheppa.kit.edu/75.php

This will allow GCMs to use these solar forcing data by taking the configuration files directly from the socrates-spectral repository.

A linked socrates issue to add scripts to generate these files is here: MetOffice/socrates/issues/15

Equivalent ticket for CMIP7 historical scenario: MOSRS Socrates:#166
Equivalent ticket for CMIP6: MOSRS Socrates:#118

[mo-jmanners]

The CMIP7 future solar TSI scenario is interesting...