buckets: update bucket type and bucket-info metadata

[goanpeca]

Summary

Expose bucket access-level and bucket metadata updates through the action, separate from bucket creation/deletion and advanced bucket policies.

Why

#100 covers creating, deleting, and listing buckets, but existing buckets also need routine updates: switching between private/public access and maintaining bucketInfo metadata. These are first-class SDK fields on Bucket.update, and they are narrower than lifecycle/CORS/replication/default-retention policy management.

SDK support (already available)

• Bucket.update({ bucketType })
• Bucket.update({ bucketInfo })
• B2Client.createBucket({ bucketInfo })
• BucketInfo.revision
• UpdateBucketRequest.ifRevisionIs

Proposed surface

New action or mode such as action: bucket-update with inputs:

• bucket-type (allPrivate / allPublic)
• bucket-info (JSON object of key/value metadata)
• if-revision-is (optional optimistic-lock revision)

Acceptance criteria

• A workflow can change an existing bucket between private and public access where B2 permits it.
• A workflow can set/replace bucket bucketInfo metadata.
• Optional if-revision-is maps to the SDK optimistic-lock field.
• Existing bucket policy issues (bucket lifecycle rules: get and set #101-bucket defaults: default encryption and default retention #105) remain scoped to their own settings.
• Tests cover type-only, metadata-only, and optimistic-lock failure paths.

Out of scope

• Creating/deleting buckets, tracked in buckets: create, delete, and list buckets #100.
• Lifecycle/CORS/replication/default encryption/default retention, tracked separately.