filter_kubernetes: add kubernetes_namespace metadata #8581

Job	Run time
run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, gcc)	12m 20s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, clang)	12m 11s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, gcc)	11m 34s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, clang)	11m 35s
run-ubuntu-unit-tests (-DFLB_SMALL=On, gcc)	11m 43s
run-ubuntu-unit-tests (-DFLB_SMALL=On, clang)	12m 25s
run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, gcc)	11m 47s
run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, clang)	11m 43s
run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, gcc)	11m 54s
run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, clang)	12m 1s
run-ubuntu-unit-tests (-DFLB_COVERAGE=On, gcc)	43m 14s
run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, gcc)	11m 44s
run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, clang)	11m 42s
run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, gcc)	11m 40s
run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, clang)	11m 32s
run-macos-unit-tests (-DFLB_JEMALLOC=Off)	10m 6s
run-macos-unit-tests (-DFLB_SANITIZE_MEMORY=On)	11m 53s
run-macos-unit-tests (-DFLB_SANITIZE_THREAD=On)	11m 42s
Unit tests (matrix)	1s
	4h 2m 47s

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