Updates #1699.
Adds a new package, `features`, which exposes methods to set and check if various internal features are enabled. The implementation uses global state to store the features so that services embedded in another service do not each require their own features map in order to check if something is enabled.
Requires a `boulder-tools` image update to include `golang.org/x/tools/cmd/stringer`.
Introduces the `authorizationLifetimeDays` and `pendingAuthorizationLifetimeDays` configuration options for `RA`.
If the values are missing from configuration, the code defaults back to the current values (300/7 days).
fixes#2024
Roland Bracewell Shoemaker