Allow arbitrarily many models in a single CSET run

[jfrost-mo]

What problem does your feature request solve?

Currently we are limited to 10 models, due to hard coding the rose-meta.conf file with this many sections. If you want to run more than that you are required to first modify the rose-meta.conf (and a single line in jinja_utils.py).

Describe the solution you'd like

Ideally we'd dynamically allow this at runtime, however rose config-edit doesn't support this. Instead we could follow the example of the RES, and have a script to generate the rose-meta.conf with the required number of models. With this it would be easier for people to add their own limit, or even for us to ship a much higher default limit (e.g. hundreds).

Describe alternatives you've considered

This might not actually be needed, as no one I've talked to can think of a case where you would be comparing more than 10 different models.

[SGallagherMet]

Just for the record, I have been contacted by people asking if the Regional Evaluation Suite could be made to do more than 10 models. It's very infrequent but it has happened in the past.