Add Base.summary(ctx), primarily to show MPI state

[nefrathenrici]

This PR adds two summary functions to give more information to the user about the context. This will be useful for debugging MPI simulations.

It would be nice to add a way to get CUDA device information, but I think we may need to make an extension when both MPI and CUDA are loaded. For now, I copied the CUDADevice assignment code to show the accurate MPI state, but this should probably be spun off into its own function to avoid duplicating code

Basic script:

import MPI, ClimaComms #, CUDA
# ENV["CLIMACOMMS_DEVICE"] = "CUDA"
ctx = ClimaComms.context()
@show ctx
ClimaComms.init(ctx)
print(summary(ctx))

[nefrathe@hpc-21-14 ClimaComms.jl]$ julia --project=test test/summary.jl 
ctx = ClimaComms.SingletonCommsContext{ClimaComms.CPUSingleThreaded}(ClimaComms.CPUSingleThreaded())
Context: SingletonCommsContext
Device: ClimaComms.CPUSingleThreaded
[nefrathe@hpc-21-14 ClimaComms.jl]$ srun julia --project=test test/summary.jl 
ctx = ClimaComms.MPICommsContext{ClimaComms.CPUSingleThreaded, MPI.Comm}(ClimaComms.CPUSingleThreaded(), MPI.Comm(0x00007f3a98ef04a0))
ctx = ClimaComms.MPICommsContext{ClimaComms.CPUSingleThreaded, MPI.Comm}(ClimaComms.CPUSingleThreaded(), MPI.Comm(0x00007f119fe9c4a0))
Context: MPICommsContext
Device: ClimaComms.CPUSingleThreaded
Total Processes: 2
Rank: 0, Node: hpc-21-14.cm.cluster
Rank: 1, Node: hpc-21-14.cm.cluster
[nefrathe@hpc-21-14 ClimaComms.jl]$