docs: add changelog entries for clickhouse multi-endpoint support

Author: pinylin

changelog.d/clickhouse_endpoint_deprecation.deprecation.md

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+The `clickhouse` sink's `endpoint` configuration option has been deprecated in favor of the new `endpoints` option. While `endpoint` will continue to work for now, it is recommended to migrate to `endpoints` which supports multiple ClickHouse instances for high availability.
+
+To migrate, change your configuration from:
+```toml
+endpoint = "http://localhost:8123"
+```
+to:
+```toml
+endpoints = ["http://localhost:8123"]
+```
+
+The `endpoint` option will be removed in a future release.
+
+authors: pinylin

changelog.d/clickhouse_endpoints.feature.md

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+The `clickhouse` sink now supports multiple endpoints through the new `endpoints` configuration option. This enables high availability and load balancing across multiple ClickHouse instances. The sink will automatically distribute traffic across healthy endpoints and perform health checks to ensure reliability.
+
+When using multiple endpoints, you can configure health checking behavior through the new `distribution` option, which allows setting retry backoff parameters for unhealthy endpoints.
+
+authors: pinylin