feat: add anonymous bucket access commands

[overtrue]

Summary

• add new anonymous top-level command and subcommands (set, set-json, get, get-json, list, links) in CLI
• wire command into parser/executor
• extend ObjectStore with bucket policy interfaces: get_bucket_policy, set_bucket_policy, delete_bucket_policy
• implement these methods in S3 client
• add support docs in help-contract tests for command and nested subcommands

Implementation details

• new module: crates/cli/src/commands/anonymous.rs
• updated entry: crates/cli/src/commands/mod.rs
• updated ObjectStore capabilities and policy methods: crates/core/src/traits.rs
• S3 bucket policy operations + error compatibility for missing-policy responses: crates/s3/src/client.rs

Verification

• cargo check -p rustfs-cli
• cargo test -p rustfs-cli help_contract -- --nocapture
• Manual acceptance on rustfs/rustfs:latest for anonymous set/get/list/links/get-json/set-json and anonymous read/write behavior

[Copilot]

Pull request overview

Adds an anonymous command group to the CLI to manage anonymous bucket/object access (mc-compatible), backed by new ObjectStore bucket policy APIs implemented for the S3 client.

Changes:

• Introduces rc anonymous {set,set-json,get,get-json,list,links} and wires it into the CLI parser/executor.
• Extends ObjectStore with get_bucket_policy / set_bucket_policy / delete_bucket_policy and adds Capabilities::anonymous.
• Implements S3 bucket policy operations with “missing policy” compatibility handling and updates CLI help-contract tests.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
crates/s3/src/client.rs	Adds Capabilities::anonymous and implements bucket policy get/set/delete on S3 client.
crates/core/src/traits.rs	Extends Capabilities and ObjectStore with anonymous/policy support.
crates/cli/src/commands/anonymous.rs	New CLI module implementing anonymous access workflows (set/get/list/links).
crates/cli/src/commands/mod.rs	Registers the new anonymous top-level command and execution routing.
crates/cli/tests/help_contract.rs	Updates help-contract expectations for anonymous and its subcommands.

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