Add raster zxy function doc #2096

Job	Run time
Build aarch64-apple-darwin	2m 58s
Build debian-x86_64	2m 19s
Build x86_64-apple-darwin	13m 26s
Build and test docker images	1m 27s
Build x86_64-pc-windows-msvc	3m 42s
Build x86_64-unknown-linux-gnu	11m 6s
Lint and Unit test	1m 36s
Test postgis:11-3.0-alpine sslmode=disable	37s
Test on macOS-latest	1m 21s
Test postgis:14-3.3-alpine sslmode=disable	34s
Test on windows-latest	1m 9s
Test postgis:15-3.3 sslmode=require	39s
Test on ubuntu-latest	1m 7s
Package	0s
CI Finished	0s
	42m 1s

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