Rename variables to workspace_variables in create mutation

Issue: Rename variables to workspace_variables in crea... (#526956 - closed)

What does this MR do and why?

Replaces the variables arg for the graphql workspaceCreate mutation with workspace_variables

• Deprecate the old variables arg
• Add new worskpace_variables arg (marked as experiment)
• Update graphql docs

The decision for this change is based on the discussion here: !184854 (comment 2401850882)

Changelog: changed EE: true

References

• #526956 (closed)
• !184854 (comment 2401850882)

Screenshots or screen recordings

This MR contains no UI changes

GraphQL mutation (workspace_variables arg)	GraphQL mutation (variables arg)

Workspace (workspace_variables arg)	GraphQL query for workspace variables

GraphQL docs

How to set up and validate locally

• Setup workspaces locally following this guide
• Run bundle exec scripts/remote_development/run-smoke-test-suite.sh, all (non-flaky) tests should still pass
• Go to the GraphQL Explorer, http://gdk.test:3000/-/graphql-explorer, and run the following query

mutation {
  workspaceCreate(input: {
    projectId: "gid://gitlab/Project/{replace-with-project-id}",
    clusterAgentId: "gid://gitlab/Clusters::Agent/{replace-with-agent-id}",
    desiredState: "Running",
    devfilePath: ".devfile.yaml",
    devfileRef: "main",
    variables: [],
    workspaceVariables: [
    { 
       key: "ENV_KEY", 
       value: "ENV_VAL", 
       variableType: "ENVIRONMENT"
     }]
  }) {
    workspace {
      id
      name
      namespace
      __typename
    }
    errors
    __typename
  }
}

• Then go to http://gdk.test:3000/-/remote_development/workspaces and open the new workspace
• Check that the workspace variables are present in the workspace as ENV variables in the terminal env | grep -i "ENV_KEY"

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