feat(drivers): implement SGCP NFS consistency group resource

[PaulJouvanceau]

Add a new resfssgcp_nfs_cg resource driver to manage Scaleway NFS consistency groups (CG). This driver provides:

• Switchover / failover of a CG to a target availability zone (AZ).
• Sync-resume to re-establish replication after an incident.
• Detailed status reporting including geo-redundancy and replication states.

Changes in util/sgcp/file.go:

• Add GetConsistencyGroup and PatchConsistencyGroup methods to the FilesAPI struct. These allow retrieving CG details and applying operations (switchover, failover, resume-replication) via the Scaleway API.

Implementation of drivers/resfssgcp_nfs_cg/main.go:

• Define data models (CgInfo, GeoRedundancyInfo, ReplicationInfo, etc.) that mirror the API response.
• Implement cgMgr to abstract API calls and handle retries.
• Implement T resource with configuration keywords: uuid, az, secret, endpoint, timeout, failover.
• Add Start(): performs switchover (or failover when --force is set), with fallback to failover on precondition failure (412) if conditions are met.
• Add SyncResume(): checks resumability via checkResumable() and calls the resume API, waiting for the CG to become ready.
• Add Status(): displays CG status, geo-redundancy targets, and replication targets with appropriate log levels.
• Implement caching (cgInfoCache) to reduce API calls during status polling.

Testing (drivers/resfssgcp_nfs_cg/main_test.go):

• Unit tests for helpers, checkResumable, localRepStatus, and waitForFn using JSON fixtures.
• Integration tests covering Start (success, 412 fallback, force, already up, operation in progress) and SyncResume (success, already resumed, in progress) using a mocked API.
• Add util/sgcpcgtesthelper package: an in-memory mock implementation of cgAPI with call counters and customisable callbacks (PatchSwitchoverFunc, PatchFailoverFunc, PatchResumeFunc). This allows precise control over API responses and state transitions.