Move health board data extraction out of model runner

[peter-t-fox]

At present, the philosophy in the code is that all observational data (cases, deaths, etc.) are fed into the InferenceFramework::Run fuction, and it extracts the data pertaining to the specific health board of interest. For example:

• [x] The select_obs function similarly has to extract data pertaining to the health board of interest

It would make more sense for the set-up code to extract and compute the necessary data structures separately, and have the Model::Run function exclusively concerned with stepping through the model iterations based on the sanitised and validated input data provided by the set up code.

The remaining locations at which health board data extraction take place are:

• [ ] Computation of the pf_byage data structure:

  const std::vector<double> pf_byage = observations.pf_pop[modelInputParameters.herd_id - 1]

• [ ] Extraction of the region's population:

  int population = GetPopulationOfRegion(observations, modelInputParameters.herd_id);

• [ ] Extraction of raw regional cases and deaths:

  const std::vector<int>& regionalCases = observations.cases[modelInputParameters.herd_id];
  const std::vector<int>& regionalDeaths = observations.deaths[modelInputParameters.herd_id];

• [ ] Determination of the age distribution for the region

  std::vector<int> agenums = ComputeAgeNums(modelInputParameters.herd_id, population, N_hcw, observations);

[github-actions[bot]]

Heads up @thibaud-porphyre @peter-t-fox - the "Covid19_EERAModel" label was applied to this issue.