[Backport release-3_40] webconnections saving as .xml: add a xmlns:x=y attribute when the http-header: prefix is used #36814

Job	Run time
build (24.04, 5, true, OFF, ON, ON, ON, ON, OFF, OFF, OFF, OFF, ON, false)	1h 37m 22s
build (39, 6, true, ON, OFF, ON, ON, OFF, OFF, ON, ON, ON, OFF, false)	2h 38m 15s
clang-tidy (24.04, 5)	6m 8s
Run tests (5, ALL_BUT_PROVIDERS)	29m 2s
Run tests (5, POSTGRES)	7m 1s
Run tests (5, HANA)	6m 36s
Run tests (6, ALL_BUT_PROVIDERS)	37m 57s
Run tests (5, ORACLE, 24.04, binary-for-oracle)	8m 26s
	5h 50m 47s

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