Add custom verification handler to NIOSSLServerHandler #2154

Job	Run time
linux (swift:5.9)	3m 32s
linux (swift:5.10)	3m 35s
linux (swift:6.0)	3m 59s
linux (swiftlang/swift:nightly-6.1-jammy)	4m 52s
	15m 58s

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