Updated migration guide with status code handling

Author: chernser

CHANGELOG.md

@@ -46,9 +46,16 @@
   previously set in milliseconds but mistakenly retrieved and used in seconds in some places. Now it correctly uses
   milliseconds consistently. (https://github.com/ClickHouse/clickhouse-java/issues/2358)
 
-- **[client-v2]** HTTP `503 Service Unavailable` responses are now surfaced as a connection-style failure (`java.net.ConnectException`) and are retried by default. Previously a `503` was treated as a server error (`ServerException`) and fell under the `ServerRetryable` fault cause. It has been moved to the `ConnectTimeout` fault cause category so that connectivity/availability failures are handled uniformly with other connection errors. Callers that specifically excluded `ServerRetryable` to avoid retrying `503` should now adjust their `client_retry_on_failures` configuration to exclude `ConnectTimeout` instead.
+- **[client-v2]** HTTP `503 Service Unavailable` responses are now surfaced as a connection-style failure (
+  `java.net.ConnectException`) and are retried by default. Previously a `503` was treated as a server error (
+  `ServerException`) and fell under the `ServerRetryable` fault cause. It has been moved to the `ConnectTimeout` fault
+  cause category so that connectivity/availability failures are handled uniformly with other connection errors. Callers
+  that specifically excluded `ServerRetryable` to avoid retrying `503` should now adjust their
+  `client_retry_on_failures` configuration to exclude `ConnectTimeout` instead.
 
-- **[client-v2]** Unexpected/unknown HTTP status codes (those the client cannot interpret as a ClickHouse response) now throw a `ClientException` instead of a `ServerException`. Since the client cannot meaningfully handle these responses, they are reported as a client-side error rather than being attributed to the server.
+- **[client-v2]** Unexpected/unknown HTTP status codes (those the client cannot interpret as a ClickHouse response) now
+  throw a `ClientException` instead of a `ServerException`. Since the client cannot meaningfully handle these responses,
+  they are reported as a client-side error rather than being attributed to the server.
 
 ### New Features
 
@@ -105,7 +112,11 @@
   supported but will be removed. Please migrate to the new property. 
   (https://github.com/ClickHouse/clickhouse-java/issues/2858)
 
-- **[client-v2]** Added `Client#cancelTransportRequest(String queryId)` to cancel an in-flight request that has not yet received a response from the server, identified by the query id supplied in the operation settings. This aborts the request on the client side (cancels the underlying IO operation) but does **not** issue a `KILL QUERY` on the server, so a query that already started executing may continue to run server-side. It is recommended to use operation timeout settings where possible; this API is intended for explicitly aborting a request from the client.
+- **[client-v2]** Added `Client#cancelTransportRequest(String queryId)` to cancel an in-flight request that has not yet
+  received a response from the server, identified by the query id supplied in the operation settings. This aborts the
+  request on the client side (cancels the underlying IO operation) but does **not** issue a `KILL QUERY` on the server,
+  so a query that already started executing may continue to run server-side. It is recommended to use operation timeout
+  settings where possible; this API is intended for explicitly aborting a request from the client.
 
 ### Improvements 
 

docs/releases/0_10_0.md

@@ -83,3 +83,13 @@ There are plans to support other HTTP clients and protocols, but they will be co
 
 This property (not a feature) is deprecated. Please use `com.clickhouse.jdbc.DriverProperties#JDBC_TYPE_MAPPINGS` (`jdbc_type_mappings`) instead.
 
+## CLIENT-V2: Service Unavailable Retry Behavior Changed
+
+Http status code `503 Service Unavailable` is handled now as `ConnectionException`. It means that if 
+retry is needed on this type of error than `client_retry_on_failures` should contain `ConnectTimeout`. 
+Previously it was under `ServerRetryable` failure cause. 
+
+## CLIENT-V2: Handling unknown status codes 
+
+New version will throw `ClientException` instead of `ServerException` on any unhandled status code. Previously 
+any such case was wrapped as `ServerException` what is not correct because it is client fails to process the code.