Add an api command

[tomasmik]

Description

This is an condensed version of #391

It works pretty much the same but does not offer any dedicated schema parsing. Instead you can parse it and explore it yourself using the graphql API. In my opinion that is sufficient.

./spacectl api 'stacks { id name }' --raw
{"data":{"stacks":[{"id":"master_stack","name":"master_stack"},{"id":"prod-infra-ireland","name":

./spacectl api \
    --variables '{"id":"aa","provider":"BITBUCKET_CLOUD","searchUsersSuggestionsInput":{"fields":null,"fullTextSearch":null,"predicates":null}}' < query
{
  "data": {
    "vcsIntegration": {
      "__typename": "VCSIntegration",
      "description": "",
      "details": {
        "__typename": "BitbucketCloudIntegration",

[mbialon]

I really liked that the previous PR added an option to fetch the schema. Could we easily add that (maybe without the filtering part)?

[mbialon]

LGTM

[alexjurkiewicz]

Thanks Tomas. Will this be released soon?

[eliecharra]

@alexjurkiewicz Sure, I'll try to find some time today to craft a release.

Actually, this is already released inside v1.20.0.