Make "docker buildx inspect" return a json string like other inspect commands in docker

[gabrieldemarmiesse]

Same reasons as #380 , for a third party lib, it's much easier to work with.

$ docker network inspect ffb3f184cd0a
[
    {
        "Name": "host",
        "Id": "ffb3f184cd0a2077f75a507320a9613eec135dc6cb234340ea924d576215e96e",
        "Created": "2020-05-04T17:50:40.0997657+02:00",
        "Scope": "local",
        "Driver": "host",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": []
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "a8d13ad9ac75a3343da098003e22052ac6ada63fa03a216e96f549f636b5ab56": {
                "Name": "gabriel_work_env",
                "EndpointID": "fe22d2b01c99eca9992079cfe1bc04774d9f1e29c4c161808273a286cc018ae7",
                "MacAddress": "",
                "IPv4Address": "",
                "IPv6Address": ""
            }
        },
        "Options": {},
        "Labels": {}
    }
]

$ docker buildx inspect blissful_swartz
Name:   blissful_swartz
Driver: docker-container

Nodes:
Name:      blissful_swartz0
Endpoint:  unix:///var/run/docker.sock
Status:    inactive
Platforms:

[gabrieldemarmiesse]

FYI docker buildx ls --format "{{json . }}" is now allowed, it duplicates some results and there is no way to know the current builder from the output, but it's still a nice improvement.

[thaJeztah]

I think it would make sense to add a --format flag here as well that supports --format=json (shortcut for --format '{{json .}}). wdyt @crazy-max ?

It's indeed not consistent with other commands, but I think the ship has sailed changing the default.

FWIW, we have been discussing introducing a new set of info (or view) subcommands to be used as a "human friendly" counterpart of inspect. While the inspect output can be useful for scripting, it's not very readable for humans. For that reason we're considering info commands that would output the information in a more opinionated, readable format. Such commands also gives us more flexibility to make improvements to the output without breaking scripts (as the output would, by design, not be intended for scripting / parsing).