Expose X-ClickHouse-Server-Display-Name header via client-v2 API

[synhershko]

Extract the server display name from HTTP response headers and surface it through OperationMetrics, QueryResponse, InsertResponse, and CommandResponse, following the existing queryId pattern.

Closes #2347

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Note

Low Risk
Additive API surface that only reads and exposes a small, whitelisted set of response headers; minimal impact on request/response flow aside from extra header collection.

Overview
Client-v2 now captures a whitelisted set of ClickHouse HTTP response headers and attaches them to operation results.

Client passes collected headers into QueryResponse and InsertResponse, while QueryResponse, InsertResponse, and CommandResponse expose getServerDisplayName() (from X-ClickHouse-Server-Display-Name) plus getResponseHeaders() for the full collected map. HttpAPIClientHelper adds collectResponseHeaders() with a fixed whitelist to avoid exposing arbitrary headers.

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[chernser]

Good day, @synhershko !
Thank you for the contribution!
Please see my comment.

Thanks!

[synhershko]

@chernser updated

[chernser]

Thank you @synhershko !