Minor environment touch ups

What does this MR do and why?

Set isEnvironmentStopping to true upon stopping

This one was somehow missed while converting the actions over, but before an environment is stopping, we set a loading indicator to ensure environments aren't double-stopped.

We don't unset it on success, as polling will remove the environment from the page once the stopping has completed.

Find errors correctly when deleting an environment

The error message was not fetched appropriately when trying to see if there were any errors upon deleting an environment.

This corrects that, as apollo shoves the errors into the following shape:

{
  data: {
    deleteEnvironment: {
      errors: [messages]
    }
  }
}

This is now also tested for.

Screenshots or screen recordings

Screencast_2022-02-18_12_00_45

Screencast_2022-02-18_12_03_03

How to set up and validate locally

1. Enable the invite modal

   Feature.enable(:new_environments_table)

2. Create an environment
3. Stop the environment
4. Delete the environment

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