Remove the dependency on the `storage.bucket.get` permissions

Description

At the moment, geddit requires the GCP user to have the storage.bucket.get permission. This is not required for getting the contents of an object and also isn't a permission of the predefined role roles/storage.objectViewer.

Remove the dependency of geddit on the storage.bucket.get.

Further details

Came across the permissions issue when trying to solve https://gitlab.developers.cam.ac.uk/uis/devops/gcp-deploy-boilerplate/-/issues/55.

Acceptance criteria

• geddit GCP fetcher no longer requires storage.bucket.get.

Links/references

https://cloud.google.com/storage/docs/access-control/iam-roles#standard-roles