Adapt CDDS for CMIP7 production work

[matthew-mizielinski]

Feature ticket for CDDS adaptation to CMIP7 standards

Targets:

• Minimal changes to Request config file necessary
• Assume variables file with have lines of the form

# <miptable (realm)>/<branded variable name>@<frequency>:stream
atmos/tas_tavg-h2m-hxy-u@mon:ap5
atmos/tas_tavg-h2m-hxy-u@day:ap6

We may have to include a region field in the above, but as this will be glb for the vast majority of variables lets hold off including this initially.

Known issues that are expected to need addressing:

• default streams code cannot just rely on mip table and variable name

[mo-jareddrayton]

Now that v3.3.0 is released I think we can dispense with using feature branches for development.

As this issue already has several CMIP7 sub-issues we can add the rest and use this to track CMIP7 progress within the v3.4.0 milestone.

Will close #567 as a duplicate.