Decouple Sphinx from Porta for container images

Currently, Sphinx deployment (`system-sphinx`) uses Porta image. Primarily, that's because:

• we use Thinking Sphinx interface to start the sphinxd daemon
• we need porta to generate sphinx configuration, again through Thinking Sphinx

The purpose of this task is to decouple Sphinx from porta to have two different images:

1. Porta image
Includes all Ruby dependencies and the Porta code, no sphinx service needs to be installed on it.

2. Sphinx image
This one would only have the sphinx service, it does not need to have any Ruby or porta code. What sphinx requires is the configuration file though, that we still need to generate with help of Thinking Sphinx. The easiest option is to generate it in the persistent volume via an initContainer running Porta image, but we can look into different options.

This separation will allows us to have container images that only have what they need, and potentially use different base images.