SPA Tests: Scaled external SPA docker setup

As part of DEV-1837 an external SPA dockerized container setup was introduced in ce for running integration tests.

However, the solution has two limitations:

• The setup works only on Jenkins (as the magnolia host is derived from dig command). For local test run, the changes need to be done manually (or by exposing magnolia port on router).
• The setup works only in single instance mode, with a hardcoded port 8080 for magnolia. This can in some cases lead to test failures, if the SPA test is running on a magnolia instance with another port

As part of the ticket:

• Local setup should work automatically
• A scaled setup for ce and dx-core should work on Jenkins