Allow pinning of sub tests

[bep]

First, thanks for this great tool. I especially love the "pinning support", and that feature would be perfect if i could also somehow filter sub-tests (t.Run ..., see below).

Since these tests may have dynamic names, I don't see how you could automate this, but how about adding an optional text input box so the user can append a filter? (not sure if that's even possible, but it would be pretty great).

func TestPinTest(t *testing.T) {
	t.Run("Variant1", func(t *testing.T) {
		t.Fail()
	})
	t.Run("Variant2", func(t *testing.T) {
		t.Fail()
	})
	t.Run("Variant3", func(t *testing.T) {
		t.Fail()
	})
}

[bep]

I guess this is discussed better here: golang/vscode-go#1602