filter_log_to_metrics: add new option 'discard_logs' #9716

Job	Run time
run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, gcc)	13m 38s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=On, clang)	13m 36s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, gcc)	12m 54s
run-ubuntu-unit-tests (-DFLB_JEMALLOC=Off, clang)	12m 59s
run-ubuntu-unit-tests (-DFLB_SMALL=On, gcc)	12m 53s
run-ubuntu-unit-tests (-DFLB_SMALL=On, clang)	13m 38s
run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, gcc)	13m 13s
run-ubuntu-unit-tests (-DSANITIZE_ADDRESS=On, clang)	13m 27s
run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, gcc)	13m 25s
run-ubuntu-unit-tests (-DSANITIZE_UNDEFINED=On, clang)	13m 11s
run-ubuntu-unit-tests (-DFLB_COVERAGE=On, gcc)	46m 4s
run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, gcc)	12m 48s
run-ubuntu-unit-tests (-DFLB_SANITIZE_MEMORY=On, clang)	13m 5s
run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, gcc)	12m 52s
run-ubuntu-unit-tests (-DFLB_SANITIZE_THREAD=On, clang)	12m 53s
run-macos-unit-tests (-DFLB_JEMALLOC=Off)	12m 21s
run-macos-unit-tests (-DFLB_SANITIZE_MEMORY=On)	11m 58s
run-macos-unit-tests (-DFLB_SANITIZE_THREAD=On)	1h 0m 16s
Unit tests (matrix)	1s
	5h 15m 12s

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