Add raster zxy function doc #2412

Job	Run time
Lint and Unit test	59s
Build aarch64-apple-darwin	4m 18s
Build debian-x86_64	5m 19s
Build and test docker images	54s
Build x86_64-apple-darwin	15m 22s
Build x86_64-pc-windows-msvc	5m 27s
Build x86_64-unknown-linux-gnu	1m 17s
Test postgis:11-3.0-alpine sslmode=disable	25s
Test postgis:14-3.3-alpine sslmode=disable	30s
Test on macOS-latest	58s
Test on windows-latest	45s
Test postgis:15-3.3 sslmode=require	29s
Test on ubuntu-latest	40s
Package	0s
CI Finished	0s
	37m 23s

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