Add io_buffer_size to BackupEngineOptions #3778

Job	Run time
build-linux	17m 14s
check-format-and-targets	25s
build-linux-cmake-mingw	12m 20s
build-linux-cmake-with-benchmark	20m 6s
build-linux-cmake-with-folly	27m 58s
build-linux-cmake-with-folly-coroutines	32m 25s
build-linux-cmake-with-folly-lite-no-test	7m 53s
build-linux-encrypted_env-no_compression	16m 7s
build-linux-make-with-folly	28m 20s
build-linux-make-with-folly-lite-no-test	9m 58s
build-linux-release	14m 33s
build-examples	11m 1s
build-fuzzers	8m 37s
build-linux-clang10-asan	17m 14s
build-linux-clang10-clang-analyze	17m 16s
build-linux-clang10-ubsan	16m 55s
build-linux-clang13-mini-tsan	24m 31s
build-linux-clang-13-no_test_run	7m 11s
build-linux-clang-no_test_run	11m 57s
build-linux-gcc-10-cxx20-no_test_run	9m 23s
build-linux-gcc-11-no_test_run	11m 42s
build-linux-gcc-8-no_test_run	9m 0s
build-linux-mini-crashtest	29m 52s
build-linux-release-rtti	12m 27s
build-linux-static_lib-alt_namespace-status_checked	19m 44s
build-linux-unity-and-headers	13m 24s
build-macos	18m 4s
build-linux-arm	14m 38s
build-linux-java	15m 7s
build-linux-java-pmd	11m 56s
build-linux-java-static	12m 29s
build-macos-java	13m 57s
build-macos-cmake (true)	47m 35s
build-macos-java-static	18m 44s
build-macos-cmake (false)	44m 46s
build-macos-java-static-universal	19m 31s
build-windows-vs2019	53m 29s
	11h 17m 49s

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