Refactor Redis TLS options parsing to fix ActionCable configuration

What does this MR do and why?

This backports !219210 (merged) to 18-8-stable-ee.

Refactor Redis TLS options parsing to fix ActionCable configuration

Previously Redis SSL parameters cert_file and key_file were converted to the appropriate types for OpenSSL via cert and file parameters, but this was not happening for ActionCable settings. As a result if someone attempted to configure Redis mutual TLS certificates in Omnibus with omnibus-gitlab!9012 (merged), an exception would be raised:

undefined method `cert_file=' for an instance of OpenSSL::SSL::SSLContext

Extract parse_client_tls_options from Wrapper into ConfigGenerator as a public class method and call it automatically from ConfigGenerator.generate. This ensures all Redis configuration consumers (Wrapper, ActionCable, etc.) properly parse TLS options without needing separate handling.

Note that cert_file and key_file parameters are no longer needed because redis-client automatically converts the cert and key parameters into the right OpenSSL types, but preserve these parameters for backwards compatibility.

Fixes #586491 (closed)

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• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
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