Fix `EnsembleSummary` plot recipe kwarg #697

[jonathanfischer97]

In reference to #697:

• Updated the trajectories kwarg to idxs in the EnsembleSummary recipes for both Plots and Makie.
• Should now allow users to select which variables to show summary line series of, in line with what the documentation shows.

Tests

• Wasn't sure where to put tests for this, or where plotting tests are kept. Should be something like:

  idxs = (2, 3)
  ensemble_summary_plot = plot(ensemble_summary; idxs)
  @test ensemble_summary_plot.n == length(idxs)

Further considerations or to-dos

1. Was the original intention of the EnsembleSummary recipes to allow users to choose/truncate the amount of trajectories that statistics are plotted over, similar to EnsembleSimulation? (Explains the mixup with idxs)

   • If so, that functionality is missing and should be added

2. Symbolic indexing does not work any of the recipes for either EnsembleSimulation or EnsembleSummary.

   • Should be added to match the recipe of AbstractSolution.

3. Plotting state spaces via giving idxs as a Tuple rather than a Vector does not work.

   • Should also be added to match the non-ensemble solution plotting recipes, if intended by the maintainers.

4. Makie EnsembleSummary recipe doesn't show transparent ranges: Shown are 100 trajectories.

5. No user-exposed way to set the color map of EnsembleSimulation trajectories? Would like an easy way to set it to something other than random, like this: