RFR: 8350279: HttpClient: Add a new HttpResponse method to identify connections [v2]

[Volkan Yazici]

> Adds `HttpResponse::connectionLabel` method that provides an identifier for the connection.
> 
> **Implementation note:** The feature is facilitated by `HttpConnection::label`, which should not be confused with `HttpConnection::id`. This distinction is explained in the JavaDoc of both properties.

Volkan Yazici has updated the pull request incrementally with one additional commit since the last revision:

  Switch from `Optional<String>` to `String` for `HttpResponseImpl::connectionLabel`
  
  Co-authored-by: Daniel Fuchs <67001856+dfuch at users.noreply.github.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24154/files
  - new: https://git.openjdk.org/jdk/pull/24154/files/2857dde0..028999a7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24154&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24154&range=00-01

  Stats: 16 lines in 1 file changed: 0 ins; 9 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/24154.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24154/head:pull/24154

PR: https://git.openjdk.org/jdk/pull/24154