prometheus: sanitize label value for text protocol #492

Job	Run time
Test with C++20 modules enabled / test	11m 6s
Test (clang++, C++20, debug) / test	15m 25s
Test with DPDK enabled / test	22m 19s
Test (clang++, C++20, dev) / test	16m 24s
Test (clang++, C++20, release) / test	15m 1s
Test (clang++, C++23, debug) / test	17m 1s
Test (clang++, C++23, dev) / test	17m 1s
Test (clang++, C++23, release) / test	15m 56s
Test (g++, C++20, debug) / test	19m 21s
Test (g++, C++20, dev) / test	12m 8s
Test (g++, C++20, release) / test	16m 22s
Test (g++, C++23, debug) / test	19m 24s
Test (g++, C++23, dev) / test	13m 2s
Test (g++, C++23, release) / test	17m 21s
	3h 47m 51s

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