Wait for service update completed

[WTFKr0]

Description

Add a way to wait for service update result
I think this is useful for Continous Deployment tools
Today we have to query service api to get the "UpdateStatus" info waiting for result

Steps to reproduce the issue:

1. docker service update --image myimage:version my_service

Describe the results you received:
my_service (code 0) in a second

Describe the results you expected:
With a new flag, wait for end of update and return status of update or RC like
0 : completed
1 : paused
2: rolledback

[fntlnz]

@WTFKr0 If you need a quick way to obtain the status using the cli you can still inspect the service's UpdateStatus

✔ 15:57:46 ~ $ docker service inspect -f "{{.UpdateStatus.State}}" att841yyzi1x
completed

[thaJeztah]

There's a proposal currently being worked on to add "Swarm" events; see moby/swarmkit#491, which may be useful for your use case. In addition, there's a pull request that allows the CLI to switch to synchronous instead of asynchronous; #31144

[WTFKr0]

OK thanx, we can close that since this PR is OK for my needs : #31144
I follow that

[thaJeztah]

Great! Thanks for opening this issue 👍, and if you have feedback on the proposed changes in #31144, feel free to comment there