Suggestion: Accept a `Nullable` annotation name and suggest it in cases where it's missing

Error-prone itself has some checks for this, but nullaway is obviously better at it.

Given an error like this

/Users/zsweers/dev/slack/restructure/slack-android-ng/libraries/foundation/slack-commons/src/main/java/slack/commons/logger/DebugLogger.java:62: error: [NullAway] parameter tag is @NonNull, but parameter in superclass method slack.commons.logger.Logger.log(java.lang.String,java.lang.String,java.lang.Throwable) is @Nullable
  public void log(final String tag, final String message, final Throwable throwable) {
                               ^
    (see http://t.uber.com/nullaway )

I'd like to be able to define my desired @Nullable annotation as an option and have nullaway suggest adding the annotation.

Start by reproducing the NullAway diagnostic shown for DebugLogger.java and inspect the superclass Logger.log signature and the existing annotation-related checks. The work is done when a configured Nullable annotation name is accepted and NullAway suggests adding it where the diagnostic identifies a missing nullable annotation.