Implement `SSL_CONF_cmd` `VerifyMode` command. #192

Job	Run time
Clippy nightly (optional)	31s
Build+test (stable, ubuntu-24.04)	1m 38s
Clang Tidy	10s
Build+test (stable, ubuntu-22.04)	1m 46s
Clippy	1m 8s
Build+test (beta, ubuntu-24.04)	1m 50s
Check for documentation errors	38s
Format	7s
Miri	1m 20s
Build+test (beta, ubuntu-22.04)	1m 47s
Build+test (nightly, ubuntu-24.04)	1m 46s
Packaging	2m 41s
Valgrind	1m 59s
Build+test (nightly, ubuntu-22.04)	1m 36s
	18m 57s

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