cassandra: adds CASSANDRA_SSL_HOSTNAME_VALIDATION

[codefromthecrypt]

This adds CASSANDRA_SSL_HOSTNAME_VALIDATION with the same behavior as defined in cassandra's SSL_HOSTNAME_VALIDATION, with the same default value of true.

Thanks @priyavivek2307 for starting this on #3457. I tried to re-use that PR, but it was too old and github closed it when I tried to rebase. Thanks also to @ankit-gautam23 for the review.

[codefromthecrypt]

I noticed this was still in our yaml, though being dead for years, so I removed it.

[codefromthecrypt]

flake is unrelated and I'll sort it out today or tomorrow. Seems a race and odd that awaitility isn't solving it..

 05:28:55,361 INFO  [armeria-common-worker-epoll-2-3] eureka.EurekaUpdatingListener (EurekaUpdatingListener.java:175) - Registered fv-az532-522 to Eureka: http://localhost:32770/eureka/v2
Error:  Tests run: 2, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 11.12 s <<< FAILURE! -- in zipkin2.server.internal.eureka.ITZipkinEureka
Error:  zipkin2.server.internal.eureka.ITZipkinEureka.registersInEureka -- Time elapsed: 0.176 s <<< FAILURE!
org.opentest4j.AssertionFailedError: Response{protocol=http/1.1, code=404, message=, url=http://localhost:32770/eureka/v2/apps/ZIPKIN}

[codefromthecrypt]

maybe got the flake 🤞