Re-implement the `GCPBackendUploader` with `cloud-storage` crate in aggregator

[jpraynaud]

Why

The current cloud-storage crate that we use for uploading files to GCP is unmaintained. We want to replace is with another crate which has better support: gcloud-storage.

What

Implement a new version of the file_uploader/gcp_uploader in the aggregator with the gcloud-storage crate.

How

• Rename gcp_uploader module to gcp_uploader_legacy and GcpBackendUploader to GcpBackendUploaderLegacy
• Create a new gcp_uploadermodule and GcpBackendUploader with gcloud-storage crate with the same features
• Update infra and documentation if the configuration has changed
• Deprecate the gcp_uploader_legacy module
• Once the new uploader is deployed on testing-preview and works as expected, remove the gcp_uploader_legacy module