feat: multiple inline environments

[Duologic]

With inline environments, we are now blocking the ability to handle multiple inline environments in. This PR proposes a solution to that. This also resolves #432.

Example Jsonnet:

{
  main(namespace, cluster)::
    (import 'main.libsonnet')
    {
      _config+:: {
        namespace: namespace,
        cluster_name: cluster,
      },
    },

  env(cluster, apiServer):: {
    local this = self,
    apiVersion: 'tanka.dev/v1alpha1',
    kind: 'Environment',
    metadata: {
      labels: {
        cluster: cluster,
      },
      name: '%s.%s' % [self.labels.cluster, this.spec.namespace],
    },
    spec: {
      apiServer: apiServer,
      injectLabels: true,
      namespace: 'kube-system',
    },
    data: $.main(self.spec.namespace, cluster),
  },

  envs: {
    dev: $.env('dev-eu', 'https://4.3.2.1'),
    qa: $.env('qa-us', 'https://1.2.3.4'),
  },

  // tk eval -e specs <this file>, get specs without the data
  // tk env should probably do something like this
  specs:: std.mapWithKey(
    function(k, obj)
      obj { data:: {} },
    $.envs
  ),
}

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Duologic]

This is function is now only used in cmd/tk/env.go:envSetCmd(), which has no affinity with inline environments.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Duologic]

This will be superseeded in the near future.