saveAsCustomOutput and customInput shouldn't require a name.

[jabrouwer82]

None of the other transformation methods on SCollection or ScioContext require a name to be used, they're all capable of generating a name using private scio internals. My team is writing an internal library utilizing scio and it would be very useful for us to be able to let the name be generated so that we don't have to pass the burden on to our users.

[jabrouwer82]

Alternatively, perhaps additionally, it would be nice if we could access CallSite in some way to explicitly generate a unique name the same way everything else does!

[jabrouwer82]

Neville Li helped me understand these can be trivially implemented as SCollection.internal.apply(transform) in our own code base.