swarmctl susceptible to 4MB grpc message limit

Please mark this low priority. Just planting a post for swarmctl to indicate that it too seems to be affected by the likes of https://github.com/moby/moby/issues/37997.

Discovered this issue when it occurred to me that swarmctl might be used to prune excessive swarmkit objects that trigger the issue, thereby removing the immediate need to change engine versions. The work-around for swarmctl is the same as for dockerd: use an older one without the 4mb grpc message limit.

My specific need is on config list, but as indicated by the above moby issue, other calls are likely affected.

Steps to recreate issue on config list:

setup:

truncate -s 511999 bigconfig.txt
cat bigconfig.txt | swarmctl config create big1
cat bigconfig.txt | swarmctl config create big2
cat bigconfig.txt | swarmctl config create big3
cat bigconfig.txt | swarmctl config create big4
cat bigconfig.txt | swarmctl config create big5
cat bigconfig.txt | swarmctl config create big6
cat bigconfig.txt | swarmctl config create big7
cat bigconfig.txt | swarmctl config create big8
cat bigconfig.txt | swarmctl config create big9

experience:

$ swarmctl config ls
Error: grpc: received message larger than max (4692733 vs. 4194304)

Affected Versions

client:

$ swarmctl version
swarmctl github.com/docker/swarmkit v1.12.0-2067-gebfb0aa1

server: dockerd 18.09.2-ce

Start with the swarmctl config ls entry point and reproduce the reported failure after creating nine 511999-byte configs with config create. Compare the client and server versions and the linked Moby issue to understand the 4MB gRPC limit. Done means the affected config operation no longer fails for the reported setup, with the supported workaround or limitation documented.