[bug] GCP initialization issues for skyplane - Policy update access denied.

[ShishirPatil]

Describe the bug When initializing skyplane, GCP errors out with the following "Policy update access denied."

To Reproduce skyplane init --reinit-gcp or skyplane init

Work Around skyplane-manual principal should be elevated to have Google Cloud Storage Admin privileges manually from the GCP console.

Error Log

Configuring GCP:
    Do you want to configure GCP support in Skyplane? [Y/n]: Y
    GCP credentials will be re-initialized
    GCP credentials found in GCP CLI
    GCP credentials found, do you want to enable GCP support in Skyplane? [Y/n]:
    Enter the GCP project ID [redacted]:
    Using GCP service account skyplane-manual
    Error saving GCP region config
    <HttpError 403 when requesting https://cloudresourcemanager.googleapis.com/v1/projects/redacted:setIamPolicy?alt=json returned "Policy update access denied.". Details: "Policy update access denied.">
Traceback (most recent call last):
  File "/home/shishirpatil_berkeley_edu/skyplane/skyplane/cli/cli_impl/init.py", line 312, in load_gcp_config
    auth.save_region_config()
  File "/home/shishirpatil_berkeley_edu/skyplane/skyplane/utils/imports.py", line 33, in wrapped
    return fn(*modules_imported, *args, **kwargs)
  File "/home/shishirpatil_berkeley_edu/skyplane/skyplane/compute/gcp/gcp_auth.py", line 35, in save_region_config
    service_account_credentials_file = self.service_account_credentials  # force creation of file
  File "/home/shishirpatil_berkeley_edu/skyplane/skyplane/compute/gcp/gcp_auth.py", line 71, in service_account_credentials
    self._service_account_email = self.create_service_account(self.service_account_name)
  File "/home/shishirpatil_berkeley_edu/skyplane/skyplane/compute/gcp/gcp_auth.py", line 202, in create_service_account
    return retry_backoff(read_modify_write)  # retry loop needed for concurrent policy modifications
  File "/home/shishirpatil_berkeley_edu/skyplane/skyplane/utils/retry.py", line 27, in retry_backoff
    return fn()
  File "/home/shishirpatil_berkeley_edu/skyplane/skyplane/compute/gcp/gcp_auth.py", line 199, in read_modify_write
    service.projects().setIamPolicy(resource=self.project_id, body={"policy": policy}).execute()
  File "/home/shishirpatil_berkeley_edu/.py3/lib/python3.8/site-packages/googleapiclient/_helpers.py", line 130, in positional_wrapper
    return wrapped(*args, **kwargs)
  File "/home/shishirpatil_berkeley_edu/.py3/lib/python3.8/site-packages/googleapiclient/http.py", line 938, in execute
    raise HttpError(resp, content, uri=self.uri)
googleapiclient.errors.HttpError: <HttpError 403 when requesting https://cloudresourcemanager.googleapis.com/v1/projects/redacted:setIamPolicy?alt=json returned "Policy update access denied.". Details: "Policy update access denied.">

    Disabling Google Cloud support

[sarahwooders]

Fixed via #757