Introduce HttpsLayer::set_ssl_callback #678

Job	Run time
clippy	2m 1s
Cross build from macOS to Linux (x86_64-unknown-linux-gnu)	5m 24s
rustfmt	11s
Cross build from macOS to Linux (FIPS) (x86_64-unknown-linux-gnu)	6m 32s
Test (stable)	2m 10s
Test features	7m 14s
Test (arm-android)	1m 59s
Test FIPS integration	3m 0s
Test (arm64-android)	2m 7s
Test (i686-android)	2m 7s
Test (x86_64-android)	1m 59s
Test (aarch64-ios)	4m 54s
Test (aarch64-ios-sim)	7m 51s
Test (x86_64-ios)	9m 16s
Test (i686-linux)	2m 20s
Test (arm-linux)	2m 13s
Test (aarch64-linux)	2m 19s
Test (arm64-macos)	4m 29s
Test (x86_64-macos)	7m 15s
Test (x86_64-mingw)	6m 6s
Test (i686-msvc)	6m 37s
Test (x86_64-msvc)	5m 17s
	1h 33m 21s

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