Learn diagnostics system by returning photolysis fields as diagnostics

### Are there any linked Issues or Pull Requests?

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### Brief description

Hi Zubair,

As you mentioned before, the dry diameter would not be a good example diagnostic to get on with, since they are already labelled as "prognostic" fields in lfric_apps.

Mohit suggested that adding a couple of extra photolysis fields would probably be a useful way of learning the pipework involved in the diagnostics.

Would it be possible for you to add these four UM diagnostics into lfric_apps with UM stashcode and UM variable name below
50-228 (jO1D)
50-229 (jNO2)
50-245 (jO2)
50-246 (jO3(P))

I think they should already be part of "photol_rates" in the lfric_apps kernel and algorithm

Kind regards,

Alan

### Further details of the issue.

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