Instead of showing untrusted configuration items one by one, collect all
of them into one batched ask with 4 options:
- apply the configuration wholesale **for now** (yes)
- apply the configuration wholesale and trust it permanently (allow
permanently)
- selectively choose subset (no)
- rejecting the configuration wholesale (no to all)
Note that we do not offer options to reject permanently a configuration,
that's what `--no-accept-flake-config` is for.
Individual prompts gain a new option to distinguish "yes for now" and
"yes forever".
Fixes#682.
Change-Id: I2492717ac277af33ea4ac9b1a11bd7d6d1bfe0db
