Fix Redis svc templating when release name includes 'redis'

What does this MR do?

Fix the templating of the Redis host via service name, when the Helm release name includes 'redis'.

1. Bring in logic from bitnami/redis chart's redis.fullname, which strips out 'redis' prefix if contains .Chart.Name .Release.Name
2. Update spec/helm_template_helper.rb to be able to optionally pass the Helm release name.
3. Add tests to spec/configure/redis_spec.rb to check that the names behave as we expect, and the the rendered configuration files match those names.

Related issues

!1773 (merged)

Checklist

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• Test plan indicating conditions for success has been posted and passes
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