Add Aqua to tests

[gdalle]

Aqua.jl is cementing itself as an important tool for testing the quality of a code base.
It would be cool to have an option that generates test/runtests.jl with Aqua built-in, like so:

using Aqua
using MyPackage

@testset verbose = true "MyPackage.jl" begin
    @testset verbose = true "Aqua.jl" begin
        Aqua.test_all(MyPackage)
    end
    # actual tests
end

[gdalle]

@nickrobinson251 I tried my hand at an easier plugin with #412, but for this one I'd actually need to modify an existing file created by the test plugin instead of creating it from scratch. Any good example I should look at?

[gdalle]

Crap I also need to modify a whole bunch of TOMLs because it requires Aqua as a test dependency

[gdalle]

Gonna try to do this by adding an aqua option to the Tests plugin