CAMEL-24359: doc-sync backported upgrade-guide entries to main

[davsclaus]

Summary

Doc-sync the camel-atmosphere-websocket header rename upgrade-guide entries from the backport PRs back to main, per the backport upgrade-guide policy.

• Adds the CAMEL-24359 entry to camel-4x-upgrade-guide-4_18.adoc (4.18.3→4.18.4 section)
• Adds the CAMEL-24359 entry to camel-4x-upgrade-guide-4_14.adoc (4.14.8→4.14.9 section)

Related PRs:

• CAMEL-24359: camel-atmosphere-websocket - align Exchange header constant names with Camel naming convention #25366 (original, merged to main)
• [backport camel-4.18.x] CAMEL-24359: camel-atmosphere-websocket - align Exchange header constant names with Camel naming convention #25382 (backport to camel-4.18.x)
• [backport camel-4.14.x] CAMEL-24359: camel-atmosphere-websocket - align Exchange header constant names with Camel naming convention #25383 (backport to camel-4.14.x)

Claude Code on behalf of davsclaus

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