A while back I noticed some unnecessary nil checking code in `flyteadmin`'s gRPC API handlers. I also noticed many many warnings about copying protobuf structs so I finally found some time to fix that up. PR is a bit of a doozy since there was a lot of plumbing of protobuf struct copies: https://github.com/flyteorg/flyte/pull/5717

Cc @acceptable-policeman-57188

holy guacamole, thank you for this! we explicitly had to disable lint checks because of all the warnings so this is really fantastic for ensuring we can keep the codebase tidy

Awesome @clean-glass-36808!!