NIFI-8410: Enabling TLS in RedisStateProvider

[gresockj]

Description of PR

This adds a property "Enable TLS" to the RedisStateProvider (see state-management.xml for further documentation). This allows a secured NiFi instance to use its own SSL context in the Redis connection provided by the RedisStateProvider. If set to "false" (the default), an insecure Redis connection will be used, regardless of whether the NiFi instance is TLS-enabled itself. If this property is set to "true" on an insecure NiFi instance, the state provider's validation will fail (since there is no SSL context to use), preventing the instance from starting up.

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[exceptionfactory]

Thanks for the work on this @gresockj! I only found a small grammatical issue, the implementation looks good!

[exceptionfactory]

Thanks @gresockj, looks good! +1 Merging.