Create datasets parameterisation list from `rose-suite.conf[model_runs]` sections

[NParsonsMO]

The Cylc / Rose team showed me how to do this by putting a basic python (cannot import yaml if we want to maintain portability) script equivalent to CMEW.app.add_datasets.bin.add_datasets_to_share.process_naml_file into CMEW/lib/python/ and then picking a facet of each dictionary (suite_id) to label each section.

I don't fully remember the implementation, but it ended up with model_runs=u-bv526,u-cw673,, which looks like the format needed for parameterisation in #392.

Acceptance criteria:

• Given suite IDs in rose-suite.conf datasets namelists
• When CMEW starts
• Then parametrisation should get generate its datasets list from the new namelists, and not from SUITE_ID/REF_SUITE_ID

Out of scope:

• Do not remove SUITE_ID/REF_SUITE_ID as they will still be needed. These will be removed by Remove variables from rose-suite.conf and use details from model_runs.yml instead #384