Orchestrator column

[silvin-lubecki]

- What I did
To perform administration tasks more easily, I added an ORCHESTRATOR column in the docker stack ls command.

⚠️ Depends on #903 ⚠️

- How I did it
I added a column in the Stack formatter, and hardcoded the orchestrator in each list command implementation.

- How to verify it

$ DOCKER_ORCHESTRATOR=kubernetes docker stack ls
NAME                SERVICES            ORCHESTRATOR
mystack             3                   Kubernetes

$ DOCKER_ORCHESTRATOR=swarm docker stack ls
NAME                SERVICES            ORCHESTRATOR
mystack             4                   Swarm

- Description for the changelog
Added ORCHESTRATOR column to docker stack ls command

- A picture of a cute animal (not mandatory but encouraged)

[vdemeester]

Seems like you have test failure 😓

[silvin-lubecki]

Don't know what you are talking about 😅

[vdemeester]

LGTM on commit 8108934

[thaJeztah]

left one comment for documentation, but otherwise looks good.

I added [WIP] to the PR title, as this depends on the other PR's being merged first

[thaJeztah]

Can you:

• Add the new Orchestrator placeholder to the "formatting" section in the docs: https://github.com/docker/cli/blob/master/docs/reference/commandline/stack_ls.md#formatting
• Update the Examples section to show the new column?

[mat007]

This should be fixed, can you PTAL? Thanks!

[thaJeztah]

LGTM after the other PR's are merged and this is rebased

[mat007]

Rebased (and squashed the doc update) !

[thaJeztah]

LGTM 👍