Support ImmersedBoundaryGrid for reading zarr output

In the [parent issue](https://github.com/CliMA/Oceananigans.jl/issues/5636) we want to measure read and write throughput in the IO-benchmark. For `ImmersedBoundaryGrid` some necessary fields for reading are not yet written by `ZarrWriter` https://github.com/CliMA/Oceananigans.jl/blob/901b2c046d04557112fa8edfc53ce6174014f251/ext/OceananigansZarrExt/zarr_writer.jl#L317-L324 I believe this needs to be fixed before we can > add read (and write) only mode to measure throughput for some (e.g. tripolar) grids.