Investigate running a single recipe under solve

[alistairsellar]

By default, REF will run every recipe for which it finds the required model/obs data. Can we constrain this to a single recipe? This could be useful if we decide that we want to to the parallelisation / workflow monitoring within cylc instead of the internal workflow monitoring of REF.

Time box: 0.5 day

[zmaalick]

We can run a single recipe by specifying the --diagnotic flag in solve command, for example:

ref solve --diagnostic enso

for more details, see documentation: https://climate-ref.readthedocs.io/en/latest/getting-started/04-solve/