Expose Metatile filename in HTTP response header #1967

Job	Run time
freebsd14 (CMake) (LLVM)	7m 29s
macos-14 (Autotools) (LLVM)	4m 48s
macos-14 (CMake) (LLVM)	9m 21s
debian:unstable (CMake) (GNU)	9s
debian:12 (Latest Mapnik) (CMake) (GNU)	4m 5s
fedora:rawhide (CMake) (GNU)	4m 3s
ubuntu:22.04 (Latest Mapnik) (CMake) (GNU)	3m 42s
ubuntu:devel (CMake) (GNU)	3m 17s
ubuntu:22.04 (Autotools) (GNU)	2m 14s
ubuntu:22.04 (Autotools) (LLVM)	2m 29s
ubuntu:22.04 (CMake) (GNU)	3m 38s
ubuntu:22.04 (CMake) (LLVM)	2m 59s
	48m 14s

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