Support GCS Objects with `/` in GCS Loaders

[vieiralucas]

So, this is basically fixing the same things as #1517 but for GCS.

Problem

When loading GCS Objects with / in the object key (eg. folder/some-document.txt) using GCSFileLoader, the objects are downloaded into a temporary directory and saved as a file.

This errors out when the parent directory does not exist within the temporary directory.

What this pr does

Creates parent directories based on object key.

This also works with deeply nested keys: folder/subfolder/some-document.txt

[vieiralucas]

@vowelparrot just added the suggested comment, also fixed the linting error.