Migrate snapshot file storage v2

[Bxota]

Description

Migrates the file storage share snapshot commands to APIv2
(/v2/publicCloud/project/{projectId}/storage/file/snapshot) and aligns the embedded
cloud_v2.json schema with the published APIv2 schema.

Snapshot routes are project scoped in v2 (they are no longer nested under a share), so:

• The parent share is now referenced through targetSpec.share.id, and snapshot list
  filters the project-wide listing on it.
• get, edit and delete check that the requested snapshot really belongs to the share
  given on the command line, so a snapshot cannot be read or deleted through an unrelated
  share ID.
• The listing columns only read targetSpec and the root resourceStatus, so a snapshot
  that is still being created — and therefore has no currentState yet — is listed like
  any other one instead of aborting the whole listing.
• A snapshot inherits the region of its parent share: targetSpec has no location, so the
  extra GET on the share that was only there to resolve the region is gone.

Schema alignment (internal/assets/api-schemas/cloud_v2.json):

• FileStorageSnapshotCurrentState: snapshotSize renamed to size, shareProto and
  shareSize removed (they are not part of the contract).
• FileStorageSnapshotTargetSpec: location removed, share is the only required field.
• Request/response examples updated accordingly.

Command changes:

• snapshot create now goes through the shared creation helper, so it supports --from-file,
  --init-file and --editor, validates the payload client-side, and accepts --wait.
  Creation is asynchronous, so the default output now reports that creation started.
• snapshot edit <share_id> <snapshot_id> is added (PUT, name and description), with
  --editor and --wait.
• snapshot delete reports that the snapshot is being deleted, matching its asynchronous
  behavior.
• The --region persistent flag is removed: it only fed the v1 region discovery, which no
  longer exists now that every file storage route is project scoped.

The detail template only referenced fields that do not exist in the API and crashed on a
snapshot whose currentState is still null (right after creation); it now renders the real
fields and degrades gracefully.

Also removes 17 stale doc/ovhcloud_cloud_storage-file_*.md files left over from the
storage-file -> storage file command rename, and regenerates doc/.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (improvement of existing commands)
• Breaking change (fix or feature that can break a current behavior)
• Documentation update

Breaking change: the --region flag of ovhcloud cloud storage file is removed.

Checklist:

• My code follows the style guidelines of this project
• I have commented my code
• I ran go mod tidy
• I have added tests that prove my fix is effective or that my feature works