Update data models based on outcome of schema review sessions

[jonssonchristian]

• Rename the "Result" class to "Dataset"
• Expand and refine the description of fields in the new "Dataset" class
• Add 'minute' as a possible dataset dimension
• Include a separate definition of an exceedance level statistic type that allows specifying a custom exceedance level
• Make a reference meteorological dataset have a list of locations rather than a single location
• Add data period and time resolution to the reference meteorological dataset schema
• Make it possible to use the IEA Wind Task 43 WRA Data Model for reference meteorological datasets for masts with sufficient metadata available
• Make the time resolution definition more flexible by having a unit and a value
• Rename data recovery rate to data availabilty, as we agreed the latter is clearer
• Make the description field for an operational restriction required, since the specification of a restriction will not say much with only a label
• Add UTC offset field at the top level of the data model to specify time zone for any data where that is relevant
• Make wind speed and direction probability distribution required under the wind resource assessment
• Add explanations under the different wind resource assessment result quantities to describe the dimensions and coordinates that should be included as standard
• Update field constraints to make empty lists and strings invalid where empty values do not make sense or should not be allowed
• Update float field constraints not to include infinity and nan values
• Move class definitions in the Python package from the "enums" module to the modules with matching topic

[jonssonchristian]

Hi @AlinaBurmesterRWE , @stephenholleran and @jonnyboxkite, would one of you be able to review this PR, which comprises the changes discussed during the last few schema review sessions? I appreciate there are quite a lot of changes. Quite a bit of it is just renamings and other refactoring.

[jonssonchristian]

I have pushed some updates to this PR, with a few refinements I realised I wanted to implement after I had first created it. I am now done with it and do not expect to change anything further. It is ready for review.

[jonssonchristian]

I now also implemented the additions and changes we agreed during the schema review session on the 14th of November.

If anyone has time to undertake at least a brief high-level review of this PR, that would be brilliant.

[jonssonchristian]

@Raggey, I had not included you in my original request to review this PR as you were not in the list of contributors then. I sent you a new invite and you seem to have access now. If you have some time to do a high-level review of this PR, that would be brilliant, but no worries at all of course if you do not. I thought I ask in any case as you said you might be able to stay involved. As per my other comments, there are a lot of changes, but a lot of it is just renaming, tidying up and other refactoring.

[jonssonchristian]

Since no one volunteered to review this, I will merge it now without review, to allow development work to progress. As discussed and agreed previously in the EYA DEF group meetings, it is not critical to have code review at this stage, where the schema and python tools are under very active development and have not been released yet. Once we have released a first version, I think we should make code review mandatory on all PRs.