840: Set GCS credentials to None if invalid service account creds provided

[freddessert]

Related Issue \ discussion

#840
https://clearml.slack.com/archives/CTK20V944/p1669932989917539

Patch Description

If an invalid a non service account credentials json is provided to the credentials, the GCS client will fail to be created, this happens when developing locally.
When passing credentials=None to storage.Client() it will fetch the environment variable GOOGLE_APPLICATION_CREDENTIALS as they recommend.
The original bug most likely stems from bucket_config.py setting the credentials via the global variable described above.

Testing Instructions

1. Authenticate your local Google Cloud environment as described in the Google Documentation.
2. Create a ClearML Dataset with an output_uri set to a GCS bucket location you have access to.
3. The ClearML Dataset is successfully created.

Other Information