[Storage] Error out when no access to the bucket during storage mounting

[Michaelvll]

We should error out when storage mounting fails on the remote VM. The following case reproduce the error:

1. Having an AWS SSO setup
2. Launch a VM on fluidstack with a private s3 bucket mounted
   Since the SSO setup will not upload the credential to the remote VM, the mounting of the s3 bucket will fail silently due to the access issue. We should fail directly for that to make the issue more easy to identify.

[romilbhardwaj]

Related - #1895

[shethhriday29]

Addressed by #3400 (currently in review process)

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