Werk #16473: Support host & service labels in CSV exports again

Component	User interface
Title	Support host & service labels in CSV exports again
Date	Feb 8, 2024
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.4.0b1 Not yet released Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk Cloud (CCE), Checkmk MSP (CME) 2.3.0b1 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk Cloud (CCE), Checkmk MSP (CME) 2.2.0p22 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk Cloud (CCE), Checkmk MSP (CME)

In Werk #13729 support for labels in CSV exports was removed (among other things). Instead, for affected columns a constant "NOT_CSV_EXPORTABLE" value was exported.

This change reintroduces host & service labels as JSON serialized strings. This only relates to CSV exports, other formats are not affected.

Sample export:

"host";"host_labels"
"test";"{""cmk\/os_platform"": ""linux"", ""cmk\/os_family"": ""linux"", ""cmk\/check_mk_server"": ""yes"", ""cmk\/site"": ""test""}"
"dummy";"{""my_label"": ""works""}"
"nothing";"{}"

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