[FR] Allow tuples of Plots.text arguments to series_annotations

[anowacki]

Since v0.22.2 Plots has allowed the user to pass tuples of arguments to Plots.text as part of the annotations attribute. However, this is not possible for series_attributes, which requires either Strings or Plots.PlotText objects:

julia> using Plots

julia> plot([1, 2], [3, 4], series_annotations=[("A", :red), ("B", :blue)])

I suggest that it would be useful to mirror the support for tuples of arguments to text.

Discussed in JuliaPlots/RecipesBase.jl#72

Also relevant: #3473