feat(clickhouse sink): add multi-endpoint support with load balancing

[pinylin]

Summary

This PR adds support for multiple ClickHouse endpoints in the ClickHouse sink, enabling high availability and load balancing across multiple ClickHouse instances. The changes include:

• Adding a new endpoints configuration option that accepts a list of ClickHouse server URLs
• Deprecating the existing endpoint option in favor of endpoints
• Adding health check configuration through the new distribution option
• Implementing load balancing and automatic health checking across endpoints
• Updating all integration tests to use the new endpoints option
• Updating documentation to reflect the changes

Vector configuration

[sinks.clickhouse]
type = "clickhouse"
inputs = ["source_name"]
endpoints = ["http://clickhouse-1:8123", "http://clickhouse-2:8123", "http://clickhouse-3:8123"]
table = "logs"
database = "default"
compression = "none"

[sinks.clickhouse.distribution]
retry_initial_backoff_secs = 1
retry_max_duration_secs = 3600

[sinks.clickhouse.batch]
max_events = 1000
timeout_secs = 1

For backward compatibility, the deprecated endpoint option still works:

[sinks.clickhouse]
type = "clickhouse"
inputs = ["source_name"]
endpoint = "http://localhost:8123"  # deprecated but still functional
table = "logs"
database = "default"

How did you test this PR?

• Unit Tests: Updated existing unit tests to use the new endpoints option
• Integration Tests: Tested in a production-like ClickHouse cluster environment:
  • Cluster Setup: 3-shard, 2-replica ClickHouse cluster
  • Failover Testing: Stopped one replica nodes to verify:
    • Automatic failover to healthy endpoints
    • Health check logic properly detecting unhealthy nodes
    • Load balancing redistributing traffic to remaining healthy nodes
    • Recovery when nodes are brought back online
• Compilation Tests: Verified that the code compiles without errors
• Changelog Validation: Used the project's changelog validation script to ensure proper formatting
• Backward Compatibility: Tested that the deprecated endpoint option still works with proper deprecation warnings

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

Notes

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    • make fmt
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[github-actions]

All contributors have signed the CLA ✍️ ✅
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[pinylin]

I have read the CLA Document and I hereby sign the CLA

[rtrieu]

left a minor suggestion, but otherwise looks good!