TLS and ACL support for Redis connection

githubSupport for external Redis 6 database was implemented at release 2.11.0 GA (by this RFE) and QE was unable to test TLS because it wasn't documented (at this comment).
Also, it should be possible to specify user credentials to access external Redis, that's currently not possible.
i.e. the implementation that enables customers to use external Redis database must be improved to be able to do that in a secure way, enabling TLS (with possible certificate validation) and credentials.

Dev notes

See this comment for more information on what is required to complete this request. (It doesn't have all the necessary low level details regarding the code changes required on the backend component though)
Rabbit hole explanation here.

Release notes

  Porta

• For those using redis sentinels the :name param is now mandatory.

  Apisonator

• Redis 6+ required
• TLS and ACL features aren't compatible with Twemproxy

To Document

This adds a way to provide a CA certificate to be trusted by porta: by adding a file called config/ca_cert.pem. This is the load sequence:

1. Trust the certificate specified by the ssl_params -> ca_file in config files
2. If the above is not provided, then trust the certificate at config/ca_cert.pem or $EXTRA_CONFIGS_DIR/ca_cert.pem **
3. If the above is not provided, then trust on system certificates installed through update-ca-trust

The file ca_cert.pem can contain a single certificate or a bundle, and it'll be loaded by a Ruby OpenSSL::SSL::SSLContext instance: https://rubyapi.org/2.7/o/openssl/ssl/sslcontext#ca_file

So far this is only used for Redis but it could be extended to other integrations in the future.