CAMEL-23526: docs - sync camel-cxf 4.14 upgrade-guide entry to main

[oscerd]

Doc-sync of CAMEL-23526's 4.14 upgrade-guide entry to main

Mirrors the === camel-cxf entry added by the backport
(#23376) into camel-4x-upgrade-guide-4_14.adoc on main, so the
canonical multi-version upgrade-guide history on main stays in sync with the
camel-4.14.x maintenance branch.

• Original PR (main, 4.21): CAMEL-23526: camel-cxf - align Exchange header constant names with Camel naming convention #23326
• 4.18.x backport: [backport camel-4.18.x] CAMEL-23526: camel-cxf - align Exchange header constant names with Camel naming convention #23369 (merged); 4.18 main doc-sync CAMEL-23526: docs - sync camel-cxf 4.18 upgrade-guide entry to main #23370 (merged)
• 4.14.x backport: [backport camel-4.14.x] CAMEL-23526: camel-cxf - align Exchange header constant names with Camel naming convention #23376
• This PR: docs-only — adds the same entry to 4_14.adoc on main
  (no code or regen)

Documents on main's 4_14.adoc:

• Constant rename: operationName / operationNamespace →
  CamelCxfOperationName / CamelCxfOperationNamespace
• The cxfrs SimpleConsumer dispatch-idiom change
• The cross-transport propagation behaviour change (transport
  HeaderFilterStrategy filters Camel* headers; route must restore the
  operation header after a transport hop)

Per CLAUDE.md's backport upgrade-guide policy.

JIRA: https://issues.apache.org/jira/browse/CAMEL-23526

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PR prepared by Claude Code on behalf of Andrea Cosentino.

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