Add `dig.Name()` decorator option

[seanlafferty-ibm]

Is your feature request related to a problem? Please describe.
I have multiple named providers of the same type, and I'd like to decorate one of them

c.Provide(NewReadOnlyConnection, dig.Name("ro"))
c.Provide(NewReadWriteConnection, dig.Name("rw"))

However the decorate function doesn't have an option to target these

dig/decorate.go

Lines 159 to 162 in c8eb7b9

	// DecorateOption modifies the default behavior of Decorate.
	type DecorateOption interface {
	apply(*decorateOptions)
	}

I use this mainly for tests- replacing certain dependencies with test versions.

Is there a non-obvious way to do this? I couldn't find an example in the unit tests.

Is this a breaking change?
No, we could create a new DecorateOption

Ran into this when looking into #230

[seanlafferty-ibm]

Little clunky, but it can be achieved with a dig.Out struct

type aaa struct {
	dig.Out
	Client *http.Client `name:"client1"`
}
digContainer.Decorate(func() aaa {
	return aaa{Client: someHttpClient}
})