Integrates GCP object storage as a working storage backend for scylla sstables as well as backup storage.
Adds an abstraction layer (atm very heavily designed around the s3 client interface and usage) to allow the "storage" etc layers of sstable management to pick transparently between "s3" and "gs" providers.
This modifies the scylla config such that endpoints can optionally (through a "type" param) ref a GS backend.
Similarly with storage_options.
Also adds some IO wrapping primitives to make it more feasible to place some logic at a mid level of the implementation stack (such as making networked storage files, ranged reading etc).
Test s3 fixture is replaced (where appropriate) with an `object_storage` fixture that multiplexes the test across both backends.
Unit tests are duplicated and for the GS versions use a boost test fixture for GCS, default local fake.
Fixes#25359Fixes#26453Closesscylladb/scylladb#26186
* github.com:scylladb/scylladb:
docs::dev::object_storage: Add some initial info on GS storage
docs/dev: Add mention of (nested) docker usage in testing.md
sstables::object_storage_client: Forward memory limit semaphore to GS instance
utils::gcp::object_storage: Add optional memory limits to up/download
sstables::object_storage_client: Add multi-upload support for GS
utils::gcp::storage: Add merge objects operation
test_backup/test_basic: Make tests multiplex both s3 and gs backends
test::cluster::conftest: Add support for multiple object storage backends
boost::gcs_storage_test: reindent
boost::gcs_storage_test: Convert to use fixture
tests::boost: Add GS object storage cases to mirror S3 ones
tests::lib::gcs_fixture: Add a reusable test fixture for real/fake GS/GCS
tests::lib::test_utils: Add overloads/helpers for reading and (temp) writing env
sstables::object_storage_client: Add google storage implementation
test_services: Allow testing with GS object storage parameters
utils::gcp::gcp_credentials: Add option to create uninitialized credentials
utils::gcp::object_storage: Make create_download_source return seekable_data_source
utils::gcp::object_storage: Add defensive copies of string_view params
utils::gcp::object_storage: Add missing retry backoff increate
utils::gcp::object_storage: Add timestamp to object listing
utils::gcp::object_storage: Add paging support to list_objects
object_storage_client: Add object_name wrapper type
utils::gcp::object_storage: Add optional abort_source
utils::rest::client: Add abort_source support
sstables: Use object_storage_client for remote storage
sstables::object_storage_client: Add abstraction layer for OS cliens (s3 initial)
s3::upload_progress: Promote to general util type
storage_options: Abstract s3 to "object_storage" and add gs as option
sstables::file_io_extension: Change "creator" callback to just data_source
utils::io-wrappers: Add ranged data_source
utils::io-wrappers: Add file wrapper type for seekable_source
utils::seekable_source: Add a seekable IO source type
object_storage_endpoint_param: Add gs storage as option
config: break out object_storage_endpoint_param preparing for multi storage
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