fix: align Admin TLS trust behavior with S3 for self-signed CAs

[overtrue]

Summary

This PR fixes issue #9 by aligning Admin API TLS trust behavior with S3 behavior.

What changed

• Switch reqwest features to include both:
  • rustls-tls-native-roots
  • rustls-tls-webpki-roots
• Update AdminClient::new to:
  • keep honoring --insecure
  • explicitly enable native/webpki built-in certs
  • load and add custom ca_bundle certs when configured
• Add tests for Admin CA bundle error paths:
  • invalid CA bundle file path
  • invalid CA bundle PEM

Why

On latest main, issue #9 was still reproducible:

• trust + no insecure:
  • rc ls succeeded
  • rc admin user list failed

After this change:

• trust + no insecure:
  • rc ls succeeded
  • rc admin user list succeeded

Validation

• cargo fmt --all --check
• cargo clippy --workspace -- -D warnings
• cargo test --workspace
• Docker TLS scenario re-check against rustfs/rustfs:1.0.0-alpha.81:
  • no trust + no insecure => both fail (expected)
  • trust + no insecure => both succeed (fixed)

Closes #9.

[Copilot]

Pull request overview

Aligns the Admin API client’s TLS trust behavior with the S3 client so aliases that rely on system trust stores and/or self-signed CA bundles behave consistently (fixing issue #9).

Changes:

• Switch reqwest workspace features to enable both native-root and webpki-root trust stores.
• Update AdminClient::new to explicitly enable built-in roots and to load an optional Alias.ca_bundle PEM as an additional root.
• Add unit tests covering Admin CA bundle error paths (missing file, invalid PEM).

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 1 comment.

File	Description
crates/s3/src/admin.rs	Configure reqwest TLS roots + optional CA bundle in AdminClient::new; add tests for CA bundle failures.
Cargo.toml	Adjust workspace reqwest features to include native + webpki rustls root support.
Cargo.lock	Lockfile update reflecting new rustls native-certs dependency.

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