Interactively prompt the user about whether docs/profiling/build reporting should be enabled

Quoting the IRC discussion with @dcoutts about #2082:

```
22:29 < dcoutts_> refold: this is one of those things where I'd really like to prompt users interactively at the beginning
22:29 < dcoutts_> "the beginning" whenever that is
22:29 < dcoutts_> anonymous build reporting, docs, profiling builds
22:29 < refold> dcoutts_: we can do this when .cabal/config is created
[...]
22:31 < refold> dcoutts_: I'll add a ticket for prompting about docs/profiling/etc.
22:31 < dcoutts_> refold: right, we might have to do that carefully since it's always been non-interactive before
22:31 < dcoutts_> but I'd really like to prompt interactively for opt-in anonymous build reporting
22:31 -!- assia_t [~assia_t@74.212.183.186] has quit [Remote host closed the connection]
22:32 < dcoutts_> and these other things make sense too
22:32 < dcoutts_> to ask at the same time
```