feat(server): Support A2A protocol (apache#1762)

[Tyooughtul]

Which issue does this PR close?

Closes #1762

Rationale

A2A protocol requires JWKS support to enable secure agent authentication with multiple identity providers. This change allows agents from different tenants to authenticate using their own public keys, and supports key rotation without requiring server restarts.

What changed?

Added JWKS support for secure agent-to-agent authentication. The implementation includes a JwksClient that fetches and caches public keys from JWKS endpoints, integrated JWKS into JwtManager for multi-tenant agent authentication, and updated HTTP middleware to support asynchronous JWT decoding. Also added TrustedIssuerConfig to support configuring multiple trusted issuers.

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

1. Which tools? Grok fast
2. Scope of usage?

• I use ai for write test case and running scripts.
• Some config code to test code:

# Trusted issuers for A2A (Application-to-Application) authentication
[[http.jwt.trusted_issuers]]
issuer = "test-issuer"
jwks_url = "http://127.0.0.1:8081/.well-known/jwks.json"
audience = "iggy.apache.org"

• Some debug! to help me find bugs。

3. How did you verify the generated code works correctly?

• Compile successfully with cargo check --package server and cargo build --package server.
• Test case passed.

5. Can you explain every line of the code if asked? Yes

[hubcio]

hey! thanks for contribution - we'll check this after the weekend.