Add custom verification handler to NIOSSLServerHandler #2148

Job	Run time
linux (swift:5.9)	3m 40s
linux (swift:5.10)	3m 28s
linux (swift:6.0)	3m 58s
linux (swiftlang/swift:nightly-6.1-jammy)	4m 43s
	15m 49s

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