Providing a consistent approach to recovering from panics in HTTP handlers and GRPC services

Placeholder for issue raised by @mkaeppler in gitlab-workhorse!671 (comment 487629901)

At present, panic recovery and reporting is not handled particularly well. We should come up with a better approach.

Ideally, the implementation for HTTP and GRPC services should be similar.

Panics and recoveries should also be covered by the labkit test suite.