Add cluster-level automatic failover support (AutoClusterFailover)

**Summary**

The C++ client does not support cluster-level failover — the ability for a Pulsar client to automatically switch from a primary cluster to a secondary cluster when the primary becomes unavailable.

**Context**

The Java client has supported this since Pulsar 2.10 (May 2022) via `AutoClusterFailover` and `ControlledClusterFailover`, both built on the `ServiceUrlProvider` abstraction. The .NET client (Pulsar.Client) has also independently implemented equivalent functionality via `IServiceInfoProvider`. The C++ client still lacks this capability. Since the C++ client is the foundation for several language bindings (Node.js, Python), this gap propagates across multiple client ecosystems. Adding cluster-level failover here would bring the C++ client to parity with Java and unblock the same capability in downstream clients.

**Proposed Behavior**

1. A `ServiceUrlProvider` (or equivalent) abstraction that allows pluggable URL resolution.
2. An `AutoClusterFailover` implementation that:
- Accepts a primary service URL and one or more secondary service URLs.
- Runs a background probe task at a configurable `checkInterval` (default: 30s).
- Switches to the first healthy secondary if the primary is unreachable for longer than `failoverDelay` (default: 30s).
- Switches back to the primary once it recovers and stays healthy for `switchBackDelay` (default: 60s).
- Supports per-cluster authentication and TLS configuration.

**Use Case**

Pulsar deployments with geo-replication across multiple regions need producer clients to automatically failover to a secondary cluster when their local cluster becomes unavailable, without requiring DNS-level failover or application-level detection logic.

Bắt đầu bằng cách so sánh các triển khai Java của AutoClusterFailover và ControlledClusterFailover, cùng với thiết kế .NET IServiceInfoProvider được đề cập trong issue. Xác định abstraction ServiceUrlProvider trong C++ và hành vi failover, bao gồm các bước kiểm tra tình trạng, độ trễ, xác thực và TLS; công việc được xem là hoàn tất khi việc chuyển từ primary sang secondary và quá trình khôi phục được các test bao phủ.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.