review: build: Add nullaway from uber

[MartinWitt]

Adds nullway from uber and set the logging leveling to warning. This currently assumes our packages are correct annotated, which they are not. I disabled all errorprone checks as we don't need two tools checking the same, we only want nullaway.

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[SirYwell]

Example from the CI how the warnings look like.

Is there additional tooling support, e.g. settings to enable in IntelliJ to directly see such warnings?

[MartinWitt]

Sadly the errorprone team is strictly against creating a tool with good useability. The best we have is some community tooling see google/error-prone#444.

[MartinWitt]

As I look more into it, this view is more or less never needed and only required if a person wants to make a PR for nullablility. Qodana will report nullable issues if we add more annotations and has a goood ui.

[MartinWitt]

After a discussion, we concluded that a tool without any usability does not benefit use enough to merge it. We are going forward with Qodana null checks.