Solidify relationship between `make_selector` method docstrings

[GabrielKS]

Currently, make_selector has a unified function docstring that describes groupby and several method docstrings that describe the various signatures. A few things we might do here in the future:

• Rethink whether there should be a unified function docstring. Maybe this information should go in the ComponentSelector docstring.
• Add 'see also' links between the various methods. Two nuances here:
  • Why does this:

      - [`make_selector` given a single component instance](@ref make_selector(component::InfrastructureSystemsComponent; name::Union{String, Nothing} = nothing))

    correctly create a link to a specific method but this

      - [`make_selector` given a single component's type and name](@ref make_selector(component_type::Type{<:InfrastructureSystemsComponent}, component_name::AbstractString; name::Union{String, Nothing} = nothing))

    just links to the generic function docstring? I can't seem to find any way to get a link to the method with component_name in it; for now this is completely blocking.
  • If we want these links between methods to be complete from the PSY perspective, we have to @extref the PSY AggregationTopology method. This is doable.