Add ability to copy to existing mbtiles files (#778) #1702

Job	Run time
Build x86_64-unknown-linux-gnu	19m 50s
Build x86_64-pc-windows-msvc	27m 56s
Build x86_64-apple-darwin	14m 36s
Build aarch64-apple-darwin	14m 42s
Test Legacy DB (postgis/postgis:11-3.0-alpine, postgres, disable)	6m 13s
Test Legacy DB (postgis/postgis:14-3.3-alpine, postgres, disable)	6m 55s
Test Legacy DB (postgis/postgis:15-3.3, postgres -c ssl=on -c ssl_cert_file=/etc/ssl/certs/ssl-ce...	7m 51s
Test & package x86_64-unknown-linux-gnu	9m 25s
Test & package x86_64-pc-windows-msvc	1m 46s
Test & package x86_64-apple-darwin	4m 58s
Test & package aarch64-apple-darwin	6s
	1h 54m 18s

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