Support json output

[kolbe]

Feature Request

Is your feature request related to a problem? Please describe:

It would be nice to be able to get information about clusters in a machine-readable format, such as json.

Describe the feature you'd like:

tiup cluster display (and maybe some other commands) should support a flag like --format or --output that can accept json (and maybe other options?) as an output format.

Why the featue is needed:

I want a machine-readable output format for cluster information so I can automatically configure my application to connect to the set of tidb instances in the cluster.

Describe alternatives you've considered:

Trying to parse the output of tiup cluster display in its current format is really unwieldy and unrealistic.

Teachability, Documentation, Adoption, Migration Strategy:

[kolbe]

Here's a workaround to read the list of tidb server nodes from the cluster topology metadata file:

python3 -c "import sys,yaml; [print(h['host']) for h in yaml.safe_load(open(sys.argv[1]))['topology']['tidb_servers']]" ~/.tiup/storage/cluster/clusters/kolbe/meta.yaml

[dveeden]

I think we can close this. We have #1208 for long term solutions. And #1358 for tiup cluster display --json which is for the specific usecase mentioned here.

[AstroProfundis]

Thanks, please update in #1208 if any new idea comes.